uuid
stringlengths 36
36
| chunk_index
int64 0
24
| text
stringlengths 1
1.82k
⌀ |
|---|---|---|
f6030843-ddc2-4058-ac49-609e4dda2425
| 4 |
Colicin K does not act as a cationophore. The partial depolarization of the membrane may account for the inhibition of active solute transport caused by colicin K.
|
a53d3049-0267-4d64-9049-774d480ff0d8
| 0 |
The acid-catalyzed decompostion of phenacylcobalamin: evidence for the formation of an enol-Co(III) pi-complex intermediate. Phenacylcobalamin has been synthesized and characterized by thin-layer chromatography and uv-visible spectroscopy, as well as identification of the cobalt-containing and organic products of its cleavage in acid and base and by aerobic photolysis.
|
a53d3049-0267-4d64-9049-774d480ff0d8
| 1 |
The major organic product from all three cleavage reactions is acetophenone and the cobalt-containing product is aquacobalamin (or hydroxocobalamin, its conjugate base). In aqueous acidic solution (pH 0 to 7.3, ionic strength 1.0 M, and 25.0 degrees C), the kinetics of the formation of aquacobalamin are biphasic representing the linear sum of two exponential terms.
|
a53d3049-0267-4d64-9049-774d480ff0d8
| 2 |
The pH dependence of the first-order rate constant of both phases shows a first-order dependence on proton concentration but with an inflection point ot pH 3.55 for the faster phase and at pH 4.03 for the slower phase. This behavior is interpreted in terms of the specific acid catalyzed formation of an intermediate from both "base on" and "base off" phenacylcobalamin with different second-order rate constants for each form, followed by an intermediate decompotion step with a similar formal mechanism.
|
a53d3049-0267-4d64-9049-774d480ff0d8
| 3 |
The nature of the intermediate is discussed and it is concluded to be a pi-complex between cob(III)alamin and the enol of acetophenone.
|
1497db85-0b89-4f3d-9bfa-acfeed5236a9
| 0 |
A quantitative treatment of the kinetics of the folding transition of ribonuclease A. New experimental data and a quantitative theoretical treatment are given for the kinetics of the thermal folding transition of ribonuclease A at pH 3.0. A three-species mechanism is used as a starting point for the analysis:
|
1497db85-0b89-4f3d-9bfa-acfeed5236a9
| 1 |
U1 (slow) in equilibrium U2(fast) in equilibrium N, where U1 and U2 are two forms of the unfolded enzyme with markedly different rates of refolding and N is the native enzyme. This mechanism is based on certain facts established in previous studies of refolding. The kinetics of unfolding and refolding show two phases a fast phase and a slow phase, over a range of temperatures extending above the transition midpoint, Tm.
|
1497db85-0b89-4f3d-9bfa-acfeed5236a9
| 2 |
The three-species mechanism can be used in this range. At higher temperatures a new much faster kinetic phase is also observed corresponding to the transient formation of a new intermediate (I). Although the general solution for a four-species mechanism is complex it is not difficult to extend the three-species analysis for the special case found here, in which the fast reaction (I in equilibrium N) is well separated from the other two reactions.
|
1497db85-0b89-4f3d-9bfa-acfeed5236a9
| 3 |
At temperatures below the transition zone the slow phase of refolding becomes kinetically complex. No attempt has been made to extend the analysis to include this effect. The basic test of the three-state analysis is the prediction as a function of temperature of alpha2, the relative amplitude of the fast phase, both for unfolding and refolding.
|
1497db85-0b89-4f3d-9bfa-acfeed5236a9
| 4 |
At temperatures above Tm for which the three-state analysis must be extended to include the new intermediate I, a crresponding quanitity alpha2(cor) is predicted and compared with measured values. Data used in the three-state prediction are values of tau2 and tau1, the time constants of the fast and slow kinetic phases, plus a single value of alpha2 measured when tau2 and tau1 are well separated.
|
1497db85-0b89-4f3d-9bfa-acfeed5236a9
| 5 |
The observed and predicted values of alpha2 agree within experimental error. The analysis predicts correctly that, for these experiments, alpha2 should have the same value in unfolding as in refolding in the final conditions. The analysis also predicts satisfactorily the equilibrium transition curve from kinetic data alone. Four striking properties of the kinetics are explained or correlated by the analysis:
|
1497db85-0b89-4f3d-9bfa-acfeed5236a9
| 6 |
(a) the drop in alpha2 to a minimum near Tm as well as the delayed rise in alpha2 above Tm;(b) the vanishing of alpha1 above the transition zone; (c) the sharp drop in tau1 inside the transition zone followed by a partial leveling off outside this zone;
|
1497db85-0b89-4f3d-9bfa-acfeed5236a9
| 7 |
and (d) the passage of tau2 through a maximum near Tm. Through a comparison of observed and predicted values of alpha2, the analysis also rules out the alternative three-species mechanism U1 (slow) in equilibrium N (fast) in equilibrium U2. Finally, the temperature dependence of the amplitude for the fast reaction (I in equilibrium N) is discussed;
|
1497db85-0b89-4f3d-9bfa-acfeed5236a9
| 8 |
the behavior of I is like that of U2 and I may be an unfolded species populated at equilibrium...
|
1b27972c-f2ea-4696-9aed-f00669030c32
| 0 |
Rate enhancement specificity with alpha-chymotrypsin: temperature dependence of deacylation. The relative rate of the hydrolysis of 2-(5-n-alkyl)furoyl-alpha-chymotrypsin reaches a maximum with the propyl derivative. The Arrhenius plots for the hydrolyses of the 2-furoyl-, 2-(5-ethyl)furoyl-, and 2-(5-n-propyl)furoyl-alpha-chymotrypsins display a discontinuity, while the plots obtained with the ramaining furoyl derivatives 5-methyl, 5-n-butyl, and 5-n-amyl are linear.
|
1b27972c-f2ea-4696-9aed-f00669030c32
| 1 |
We conclude that the deacylation of the furoyl derivatives of alpha-chymotrypsin involves a minimum of two elementary reaction steps. Depending upon the reaction conditions, rate enhancement specificity appears to be either entropy or enthalpy controlled.
|
155bb8c1-a077-4c27-b25c-3471e6e550fb
| 0 |
Optimal conditions and specificity of interaction of a distinct class of nonhistone chromosomal proteins with DNA. A subclass of nonhistone chromatin proteins with high DNA affinity has been isolated from rat liver. The interaction of the isolated proteins with DNA in vitro was characterized utilizing a nitrocellulose filter binding technique.
|
155bb8c1-a077-4c27-b25c-3471e6e550fb
| 1 |
The temperature, time, concentration, ionic strength, and pH dependence were characterized. Optimal interaction was observed at 0.19 M naCl, pH 7.5 with a protein to DNA ratio of 13 (w/w). Equilibrium and kinetic competition experiments indicated that these proteins interact optimally with A-T rich and single-stranded DNA.
|
155bb8c1-a077-4c27-b25c-3471e6e550fb
| 2 |
The data also suggest that these proteins might affect the helixcoil transiton of DNA.
|
3315492f-d762-4eb1-8fbb-161b8d6187da
| 0 |
The subcellular distribution of adenylate and guanylate cyclases in murine lymphoid cells. Membrane vesicles can be prepared from murine lymphoid cells by nitrogen cavitation and fractionated by sedimentation through nonlinear sucrose density gradients. Two subpopulations of membrane vesicles, PMI and PMII, can be distinguished on the basis of sedimentation rate.
|
3315492f-d762-4eb1-8fbb-161b8d6187da
| 1 |
The subcellular distribution of adenylate and guanylate cyclases in these membrane subpopulations have been compared with the distribution of a number of marker enzymes. Approximately 20-30% of the total adenylate and guanylate cyclase activity is located at the top of the sucrose gradient (soluble enzyme), the remainder of the activity being distributed in the PMI and PMII fractions (membrane-bound enzyme).
|
3315492f-d762-4eb1-8fbb-161b8d6187da
| 2 |
More than 90% of the 5'-nucleotidase and NADH oxidase activities detected in lymphoid cell homogenates are located in PMI and PMII fractions, whereas succinate cytochrome c reductase activity is detected only in the PMII fractions. In addition, beta-galactosidase activity is distributed in the soluble and PMII fractions of the sucrose density gradients.
|
3315492f-d762-4eb1-8fbb-161b8d6187da
| 3 |
On the basis of the fractionation patterns of these various enzyme activities, it appears that PMI fractions contain vesicles of plasma membrane and endoplasmic reticulum, whereas PMII fractions contain mitochondria, lysomes, and plasma membrane vesicles. Approximately 30-40% of the adenylate and guanylate cyclase activities in PMII can be converted to a PMI-like form following dialysis and resedimentation through a second nonlinear sucrose gradient.
|
3315492f-d762-4eb1-8fbb-161b8d6187da
| 4 |
Adenylate and guanulate cyclases can be distinguished on the basis of sensitivity to nonionic detergents.
|
890caff1-30b4-41ec-b027-19c500197fec
| 0 |
Fluorine-19 nuclear magnetic resonance study of fluorotyrosine alkaline phosphatase: the influence of zinc on protein structure and a conformational change induced by phosphate binding. 19F nuclear magnetic resonance (NMR) spectroscopy has been used to study a fully active E. coli fluorotyrosine alkaline phosphatase. The fluorotyrosine resonances provide sensitive probes of the conformational states of the protein.
|
890caff1-30b4-41ec-b027-19c500197fec
| 1 |
They were used to follow the addition of zinc or cobalt to the apoprotein, and the titration of the protein with inorganic phosphate or the inhibitor 2-hydroxy-5-nitrobenzylphosphonate. The results indicate that 2 molecules of inorganic phosphate per dimer of alkaline phosphatase are required to complete a general conformational change in the protein involving perturbations to the environment of several tyrosines.
|
890caff1-30b4-41ec-b027-19c500197fec
| 2 |
Spectra of the cobalt enzyme indicate that on specific tyrosine per subunit may be near the metal site. The 19F NMR results, combined with the 31P NMR results in the accompanying paper, lead directly to the conclusion that dissociation of noncovalently bound inorganic phosphate from the enzyme is the rate-limiting process in enzyme catalysis at high pH.
|
890caff1-30b4-41ec-b027-19c500197fec
| 3 |
The local environment of the individual fluorotyrosines is also discussed.
|
f1088655-aa7a-409b-914b-941031a8d6a3
| 0 |
31P nuclear magnetic resonance study of alkaline phosphatase: the role of inorganic phosphate in limiting the enzyme turnover rate at alkaline pH. 31P nuclear magnetic resonance (NMR) was used to directly observe the binding of inorganic phosphate to alkaline phosphatase. Evidencq for the tight binding of 1.5-2.0 mol of inorganic phosphate per dimer of alkaline phosphatase is presented.
|
f1088655-aa7a-409b-914b-941031a8d6a3
| 1 |
Two distinct forms of bound phosphate are observed, one predominating above pH 7 and representing the non-covalent E-P1 complex and the other predominating below pH 5 and representing the covalent E-P1 complex. The 31P NMR line width of the E-P1 complex indicates that the dissociation of noncovalent phosphate is the rate-limiting step in the turnover of the enzyme at high pH.
|
7b101707-0240-4ef7-bbc0-967b8269140a
| 0 |
An analysis of the autophosphorylation of rabbit and human erythrocyte membranes. The autophosphorylation of rabbit and human erythrocyte membranes has been studied under various experimental conditions. The phosphopeptides of the erythocyte membranes were identified using sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis followed by ratioautography. The pattern of phosphorylatiion of membrane components differs with respect to the phosphoryl donor used (ATP or GTP) and to the pH at which the reaction is carried out.
|
7b101707-0240-4ef7-bbc0-967b8269140a
| 1 |
Both species appear to contain at least two distinct membrane-bound protein kinases. The human erythrocyte membrane contains a cyclic adenosine 3'5'-monophosphate (cyclic AMP)-dependent protein kinase and several substrates for this kinase. Only ATP can be used as a phosphoryl donor for this kinase.
|
7b101707-0240-4ef7-bbc0-967b8269140a
| 2 |
In contrast, the rabbit erythrocyte membrane does not contain a cyclic AMP dependent protein kinase but does contain a kinase which utilizes only ATP as the phosphoryl donor and is specific for certain endogenous substrates at low pH. Both the human and rabbit erythrocyte membranes contain a kinase which utilizes GTP, perhaps also ATP, as the phosphoryl donor.
|
7b101707-0240-4ef7-bbc0-967b8269140a
| 3 |
The substrates of these kinases are similar in both species.
|
de0d475d-4283-4fdc-9677-9e05154f86ea
| 0 |
Glutamine synthetase adenylyltransferase from Escherichia coli: purification and physical and chemical properties. The glutamine synthetase adenylyltransferase (EC 2.7.7.42), WHIch catalyzes the adenylylation and deadenylylation of glutamine synthetase in E. coli, has been stabilized and purified 2200-fold to apparent homogeneity. Sedimentation and electrophoresis studies show that the native enzyme is a single polypeptide chain of 115,000 +/- 5000 molecular weight with an isoelectric pH (PL) OF 4.98
|
de0d475d-4283-4fdc-9677-9e05154f86ea
| 1 |
, a sedimentation coefficient (S20.w0) of 5.6S, and a molar frictional coefficient (f/f0) of 1.52. An alpha-helical content of approximately equal to 25% and approximately equal to 28% beta-pleated sheet and approximately equal to 47% random coil structures were estimated from circular dichroism measurements.
|
de0d475d-4283-4fdc-9677-9e05154f86ea
| 2 |
The amino acid composition of the protein has been determined. The intrinsic tryptophanyl residue flourescence of adenylyltransferase is two fold greater than that of L-tryptophan; this property has been used to monitor ligand-induced conformational changes in the enzyme. Activators of the adenylylation reaction (ATP, L-glutamine, or the E.
|
de0d475d-4283-4fdc-9677-9e05154f86ea
| 3 |
coli PII regulatory protein) produced an enhancement of fluorescence; alpha-ketoglutarate, an inhibitor of adenylylation and an activator of deadenulylation, caused a net decrease in fluorescence. The adenylytransferase has separate interaction sites for L-glutamine and the regulatory PII protein.
|
f2165ce9-6167-4274-a014-43dfcc422b50
| 0 |
The esterification of dolichol by rat liver microsomes. The incubation of 1-[3H)dolichols with cell-free preparations from various rat tissues resulted in the formation of a labeled material which possessed the characteristics of synthetic dolichol palmitate. Rat liver microsomes were found to be a good source of the acyltransferase activity, and the properties of the reaction were investigated using microsomal preparations.
|
f2165ce9-6167-4274-a014-43dfcc422b50
| 1 |
The reaction did not require ATP, CoA, or Mg2+ and was stimulated by the addition of phosphatidylcholine. The esterification of dolichol appears to be similar to the esterification of retinol. The fact that the esterification of dolichol is not depressed even in the presence of a several-fold excess of retinol is evidence that the two reactions are catalyzed by different enzymes.
|
be2d5425-a486-40d6-a0e6-d842c3757e0f
| 0 |
Preparation of Fv fragment from the mouse myeloma XRPC-25 immunoglobulin possessing anti-dinitrophenyl activity. The myeloma IgA protein produced by plasmacytoma XRPC-25, was isolated by affinity chromatography on dinitrophenyllysine-Sepharose. The affinity constant of the intact protein or its Fab' toward 2,4-dinitrophenyl-L-lysine (Dnp) was found to be 2.6
|
be2d5425-a486-40d6-a0e6-d842c3757e0f
| 1 |
X 10(5) M-1. In order to prepare an Fv fragment (Hochman, J., Inbar, D., and Givol, D. (1973), Biochemistry 12, 1130) from this protein, the heavy and light chains were separated and the light chain was digested with trypsin at pH 8.2
|
be2d5425-a486-40d6-a0e6-d842c3757e0f
| 2 |
to yield half a light chain. This digest was reassociated with the heavy chain and the recombinant was digested with papain at pH 5.7. Fractionation of this digest on a Sephadex G-75 column and Dnp-lysine-Sepharose resulted in the isolation of an Fv fragment which possesses one binding site for Dnplysine (Ka = 2.0
|
be2d5425-a486-40d6-a0e6-d842c3757e0f
| 3 |
X 10(5) M-1). The active Fv fragment has a molecular weight of 23,400 and is composed of two peptide chains, each having a molecular weight of approximately 12,000. The N-terminal residues of these chains are aspartic and glutamic acids, which are also N-terminal in the heavy and light chains, indicating that the Fv is composed of VL and VH.
|
5ac5d783-ad9d-4fc2-a93f-ad7f508b4c97
| 0 |
Purification and properties of a low molecular weight protein factor of mitochondrial energy-linked functions. 1. A soluble protein with a molecular weight of 11-12-10(3) has been isolated from bovine-heart mitochondria, which stimulates the following ATP-dependent reactions of submitochondrial particles treated with 0.6 mM EDTA and 1 M NH4OH:
|
5ac5d783-ad9d-4fc2-a93f-ad7f508b4c97
| 1 |
reverse electron transfer from succinate to NAD, transhydrogenation from NADH to NADP, and ATP-Pi exchange. The factor has no effect on the NADH oxidase, succinate oxidase and ATPase activities of the particles. 2. The stimulatory effect of the factor in the ATP-dependent reduction of NAD by succinate is 12 mumol-min-1-mg-1 of the factor protein.
|
5ac5d783-ad9d-4fc2-a93f-ad7f508b4c97
| 2 |
However, the NH4OH-EDTA treated particles are saturated for maximal activation of the above reaction by very small amounts of the factor (about 20-40 mug factor per mg particle). 3. Electrophoresis of the factor preparation on polyacrylamide gels showed a single protein band plus a nonprotein material which moved at the dye front and was weakly stained with Coomassie Blue.
|
5ac5d783-ad9d-4fc2-a93f-ad7f508b4c97
| 3 |
The protein was shown to be required for activation of the particles; whether the fast-moving, nonprotein material is also required is not known. 4. The factor is inhibited by mercurials and N-ethylmaleimide. The former, but not the latter, inhibition is completely reversed by 1,4-dithiothreitol.
|
5ac5d783-ad9d-4fc2-a93f-ad7f508b4c97
| 4 |
5. The NH4OH-EDTA treated particles are also stimulated by rutamycin up to about 0.1 nmol of rutamycin per mg particle; higher rutamycin concentrations inhibit. Depending on the particle preparation, the factor stimulates up to about 3 nmol per mg particle, but does not inhibit at higher concentrations.
|
5ac5d783-ad9d-4fc2-a93f-ad7f508b4c97
| 5 |
In addition, under certain conditions in which appropriate concentrations of rutamycin fail to stimulate the particles, the factor still does.
|
67f13716-1468-4adf-84f4-f7d823a940bd
| 0 |
Effect of the transmembrane electric field on the photochemical and quenching properties of photosystem II in vivo. The intermediate phase of fluorescence relaxation (lms-ls) (Joliot, P., Joliot, A., Bouges, B, and Barbieri, G. (1971) Photochem. Photobiol. 14, 287-305), following a single saturating flash, is shown to be controlled by a slow phase of the reoxidation of Q- by a secondary acceptor and, in vivo, by the transmembrane electric field.
|
67f13716-1468-4adf-84f4-f7d823a940bd
| 1 |
The kinetics of reoxidation of Q- are slowed by lowering the pH. This slowing effect is interpreted in terms of the reversible formation at low pH of QH which is not oxidizable by the secondary acceptor. The electric field transforms Photosystem II centers into a non-quenching photochemically inactive state that cannot be attributed to an accumulation of Q-.
|
67f13716-1468-4adf-84f4-f7d823a940bd
| 2 |
Centers are unequally sensitive to the field. A critical field strength can be defined for each center above which that center is blocked and below which the center is photochemically active. The transformation from the active to inactive state occurs over a narrow range of field strength. Sensitive centers are blocked by the field in less than 1 ms and become active again in less than 10 ms as the field strength falls.
|
67f13716-1468-4adf-84f4-f7d823a940bd
| 3 |
Two hypotheses are proposed for the mechanism of blockage of centers by the field: (1) a field induced conformational change in the centers, (2) the formation or suppression of a dipole critical to the function of a center. The activity of the ATP synthetase, determining the rate of relaxation of the field, was controlled by a light-dark treatment or by a chemical method using p-benzoquinone.
|
25b23fed-217f-476a-87c6-d8369fdcad0a
| 0 |
Determination of H+/e- ratios in chloroplasts with flashing light. Using a rapid pH electrode, measurements were made of the flash-induced proton transport in isolated spinach chloroplasts. To calibrate the system, we assumed that in the presence of ferricyanide and in steady-state flashing light, each flash liberates from water one proton per reaction chain.
|
25b23fed-217f-476a-87c6-d8369fdcad0a
| 1 |
We concluded that with both ferricyanide and methylviologen as acceptors two protons per electron are translocated by the electron transport chain connecting Photosystem II and I. With methyl viologen but not with ferricyanide as an acceptor, two additional protons per electron are taken up due to Photosystem I activity.
|
25b23fed-217f-476a-87c6-d8369fdcad0a
| 2 |
One of these latter protons is translocated to the inside of the thylakoid while the other is taken up in H2O2 formation. Assuming that the proton released during water splitting remains inside the thylakoid, we compute H+/e- ratios of 3 and 4 for ferricyanide and methylviologen, respectively.
|
25b23fed-217f-476a-87c6-d8369fdcad0a
| 3 |
In continuous light of low intensity, we obtained the same H+/e- ratios. However, with higher intensities where electron transport becomes rate limited by the internal pH, the H+/e- ratio approached 2 as a limit for both acceptors. A working model is presented which includes two sites of proton translocation, one between the photoacts, the other connected to Photosystem I, each of which translocates two protons per electron.
|
25b23fed-217f-476a-87c6-d8369fdcad0a
| 4 |
Each site presents a approximately 30 ms diffusion barrier to proton passage which can be lowered by uncouplers to 6-10 ms.
|
9372c622-b5ee-472e-8cb7-18146db164ec
| 0 |
[Study of the mechanism of the effect of extracellular pH on the synthesis of the oxidative complex (cytochrome a+a3) of Bacillus coagulans: relationship to the "glucose effect" and role of excreted coproporphyrin III (author's transl)]. During the "respiratory adaptation" of Bacillus coagulans, it was possible to dissociate the kinetics of cytochrome a and a3 synthesis with carbon monoxide.
|
9372c622-b5ee-472e-8cb7-18146db164ec
| 1 |
The synthesis of cytochrome a3 is preferentially repressed when the pH of the incubation medium is pH 6.5 instead of pH 5.5. However, though the total synthesis of tetrapyrrole compounds is the same at both pH values, the excretion of coproporphyrin III is much increased at pH 6.5.
|
9372c622-b5ee-472e-8cb7-18146db164ec
| 2 |
Bacillus coagulans, sensitive to the "glucose effect", shows the "pH effect" only in the presence of high glucose concentrations. The repression of the oxidase complex synthesis by a slight increase of the extracellular pH appears directly related to the increase of the extracellular coproporphyrin III.
|
6055ad14-c1c4-4a2f-aec6-dacbf46e8232
| 0 |
The effect of retinol and retinoic acid on the testicular phospholipase a activity in retinol-deficient rats. Both phospholipases A1 and A2 activities (EC 3.1.1.4) at pH 7.4 were found to be significantly decreased in retinol-deficient rat testes supplemented with retinoic acid as compared to retinol-fed controls using 1-acyl-2-[1-(14)C]-oleoyl-sn-glycero-3-phosphocholine as substrate. However, little or no difference was observed in phospholipase A1 activity at pH 3.0 in both groups of rats.
|
c4c84c85-601d-4b91-80eb-b8ee0bc50e2a
| 0 |
Enzymatic properties of cloacin DF13 and kinetics of ribosome inactivation. 1. The cloacin DF13-induced inactivation of ribosomes in vitro can be described as an enzyme-catalyzed reaction according to the Michaelis-Menten equation. Most probably the cloacin acts as a unique endoribonuclease. 2. At pH 7.8 and 37 degrees C the Km value for the reaction of cloacin DF13 with ribosomes is 13.2
|
c4c84c85-601d-4b91-80eb-b8ee0bc50e2a
| 1 |
- 10(-6) M. If under these conditions the reaction mixture is supplemented with all components necessary for protein synthesis, the Km changes to 17.7 - 10(-6) M. 3. The in vitro activity of cloacin DF13 has a temperature optimum of 43 degrees C at pH 7.8
|
c4c84c85-601d-4b91-80eb-b8ee0bc50e2a
| 2 |
and a pH optimum of 8.4 at 37 degtees C. 4. Experiments with cloacin DF13-immunity protein as an inhibitor of the cloacin activity in vitro have indicated that the immunity protein might be considered as a non-competitive and virtually "irreversible" inhibitor.
|
e4fe945e-6088-4ebd-b83d-5c34d740b9cd
| 0 |
Transfer RNA methyltransferase activity in paramecium aurelia. The tRNA methyltransferases from Paramecium aurelia were investigated. The effects of varying the Mg2+ and NH4+ concentrations, pH, and temperature on the methylation of Escherichia coli B tRNA using extracts from P. aurelia were determined. Optimum tRNA methyltransferase activity was observed at pH 7.8
|
e4fe945e-6088-4ebd-b83d-5c34d740b9cd
| 1 |
and 37 degrees C. The Mg2+ optimum occurred at 0.66 mM in the absence of NH4+ while the NH4+ optimum occurred at 100 mM in the absence of Mg2+. Analysis of the bases methylated in (E. coli B) tRNA by extracts of P. aurelia showed the presence of 1-methyladenine, 1-methylguanine, N2-methylguanine, N2,N2-dimethylguanine and methylated pyrimidine nucleotides.
|
e4fe945e-6088-4ebd-b83d-5c34d740b9cd
| 2 |
In comparison, an analysis of the in vivo methylation of tRNA from P. aurelia showed the presence of 1-methyladenine, 6-methyladenine, 6,6-dimethyladenine, 1-methylguanine, N2-methylguanine, N2,N2-dimethylguanine, 7-methylguanine, and methylated pyrimidine nucleotides. The pattern of methylation of tRNA in P.
|
e4fe945e-6088-4ebd-b83d-5c34d740b9cd
| 3 |
aurelia is similar to that observed in other eukaryotes.
|
4818bfac-5464-4cb7-b428-97e113c524e5
| 0 |
The effect of silver ion binding and pH on the buoyant density of DNA and its use in fractionating heterogeneous DNA. 1. The effect of pH on the buoyant density of the complexes of Ag+ with DNA has been studied using 3H-labeled human DNA and several bacterial DNAs to determine the conditions necessary for the maximum resolution of compositional heterogeneity.
|
4818bfac-5464-4cb7-b428-97e113c524e5
| 1 |
In neutral CS2SO4 density gradients, Ag+ complexes with (G - C)-rich components are always denser than those with (A - T)-rich components, since (G - C)rich DNAs have a larger affinity for Ag+ than (A - T)-rich DNAs and their complexes are denser than (A - T)-rich complexes.
|
4818bfac-5464-4cb7-b428-97e113c524e5
| 2 |
In alkaline (pH greater than 9) CS2SO4 gradients, the buoyant density of the Ag+ - DNA complex is not a simple function of base composition. The Ag+ affinity of (A - T)-rich DNA is larger than that of (G - C)-rich DNA but the density of a (G - C)-rich complex is larger.
|
4818bfac-5464-4cb7-b428-97e113c524e5
| 3 |
Thus the ordering of the buoyant density changes depends on the amount of added Ag+. 2. The problem of resolving the density heterogeneity within a tracer DNA, and minor components of DNA, is explored and useful fractionation techniques are developed.
|
c815a4ee-fa3f-4faf-942d-ee2b2b8e95b8
| 0 |
Comparison of purple membrane from Halobacterium cutirubrum and Halobacterium halabium. Direct comparison of purple membrane preparations from Halobacterium cutirubrum and Halobacterium halobium was carried out. Both preparations were found to be essentially identical with respect to their molecular weight, retinal content, lipid composition, fingerprinting of peptides from peptide digestion, electron micrographs and X-ray diffraction patterns, and behaviour as a light-activated proton pump. Thus, there would appear to be no species differences in the purple membranes from these two bacteria.
|
6255917b-4472-4543-a552-8743a0f369ad
| 0 |
Kinetics of ion translocation across charged membranes mediated by a two-site transport mechanism. Effects of polyvalent cations upon rubidium uptake into yeast cells. (1) The effect of surface charge upon the kinetics of monovalent cation translocation via a two-site mechanism is investigated theroretically. (2) According to the model dealt with, typical relations are expected for the dependence of the kinetic parameters of the translocation process upon the concentration of a polyvalent cation, differing essentially from those derived for the case in which the membrane carries no excess charge.
|
6255917b-4472-4543-a552-8743a0f369ad
| 1 |
(3) Even when a polyvalent cation does not compete with the substrate cation for binding to the translocation sites, apparently competitive inhibition may occur when the membrane is negatively charged. (4) The model is tested experimentally by studying the effects of the polyvalent cations Mg2+, Sr2+, Ca2+, Ba2+ and Al3+ upon Rb+ uptake into yeast cells at pH 4.5
|
6255917b-4472-4543-a552-8743a0f369ad
| 2 |
A good applicability is found. (5) Equimolar concentrations of polyvalent cations reduce the rate of the Rb+ uptake into yeast cells in the order Mg2+ less than Sr2+ less than Ca2+ less than Ba2+ less than Al3+. (6) The conclusion is reached that the reduction in the rate of Rb+ uptake caused by the polyvalent cations applied results mainly from screening of the negative fixed charges on the membrane surface and binding to these negative sites rather than competition with Rb+ for the transport sites.
|
6255917b-4472-4543-a552-8743a0f369ad
| 3 |
(7) The results of our investigation indicate the affinity of the alkaline-earth cations for the negative fixed charges on the surface to the yeast cell membrane increases in the orther Mg2+ less than Sr2 less than Ca2+ less than Ba2+. (8) Probably mainly phosphoryl groups determine the net charge on the membrane of the yeast cell at a medium pH of 4.5
|
6255917b-4472-4543-a552-8743a0f369ad
| 4 |
.
|
aa311d47-e10c-46ce-b1f4-40897eb09cea
| 0 |
The structure of monellin and its relation to the sweetness of the protein. The sweet protein monellin [1-3] has been shown to consist of two non-identical subunits of 50 and 42 amino acid residues, which were separated electrophoretically and chromatographically. Automatic sequential Edman degradation gave the complete sequence of the longer subunit, and a partial sequency of the shorter one.
|
aa311d47-e10c-46ce-b1f4-40897eb09cea
| 1 |
It was found that the sweetness of monellin requires the undissociated molecule. The individual subunits were not sweet, neither did they block the sweet sensation of sucrose or monellin. Blocking of the single SH of monellin abolished its sweetness as did reaction of the single methionyl residue with CNBr.
|
aa311d47-e10c-46ce-b1f4-40897eb09cea
| 2 |
Since the cysteinyl and methionyl residues appear to be adjacent, it is suggested that this part of the molecule is essential for its sweetness.
|
74679521-8394-4f44-8cf7-095d5adabd2e
| 0 |
Anomalous fluorescence of yeast 3-phosphoglucerate kinase. The 3-phosphoglycerate kinase (EC 2.7.2.3) of yeast which contains two tryptophyl and eight tyrosyl residues per molecule, displayed an unusualy fluorescence emission spectrum with a maximum at 308 nm when excited at 280 nm. The emission peak shifted to 329 nm when excited at 295 nm.
|
74679521-8394-4f44-8cf7-095d5adabd2e
| 1 |
We could confirm that it was due to the efficient quenching of tryptophyl fluorescence as well as to the incomplete energy transfer from tyrosyl to tryptophyl residues. The average fluorescence quantum yield of this protein was 0.076 (excitation at 280 nm) and that of tryptophyl residues was 0.046 (excitation at 295 nm).
|
74679521-8394-4f44-8cf7-095d5adabd2e
| 2 |
As the pH of the solution was lowered, the fluorescence intensity of phosphoglycerate kinase at 329 nm dramatically increased between pH 5 and 4, while the position of the peak remained unchanged. When denatured in 4 M guanidine hydrochloride, the protein showed two emission peaks, one at 343 nm and the other at 303 nm.
|
65d3a4bb-4e81-494e-9597-55560d112b85
| 0 |
Binding of norgestrel to human plasma proteins. Binding of [14, 15-3H](+/-)-norgestrel to human plasma proteins has been investigated. Norgestrel showed greater affinity to plasma than to human serum albumin indicating specific norgestrel binding protein(s) in the plasma. alpha1-acid glycoprotein showed high affinity for norgestrel when compared with human serum albumin.
|
65d3a4bb-4e81-494e-9597-55560d112b85
| 1 |
The binding protein was eluted at pH 5.8 by step by step elution on a DEAE-cellulose column. Norgestrel binding to plasma proteins was not affected at 60 degrees C. The optimal binding occurred between pH 7 and 8. Ligand specificity of the binding protein revealed that progesterone was able to compete for the norgestrel binding sites, whereas corticosterone, testosterone, oestradiol, and norethindrone acetate did not show much competition.
|
65d3a4bb-4e81-494e-9597-55560d112b85
| 2 |
The molecular weight of the binding protein was found to be approximately 43 000. Sucrose density gradient analysis indicated that norgestrel bound to a macromolecular component of sedimentation coefficient 2.9 S. The association constant (Kass) and dissociation constant (Kdiss) of norgestrel-binding plasma protein was found to be 1.4
|
65d3a4bb-4e81-494e-9597-55560d112b85
| 3 |
-10(6) M-1 and 0.7-10(-6) M respectively. The number of binding sites was 0.5-10(-9) mol/mg protein. Norgestrel-binding protein in the plasma appeared to be a protein different from human serum albumin, corticosteroid-binding globulin and sex-steroid-binding protein.
|
65d3a4bb-4e81-494e-9597-55560d112b85
| 4 |
This binding protein showed some similarities to alpha1-acid glycoprotein.
|
25b21423-8e25-490d-a875-6bc16acc0055
| 0 |
Equilbrium and kinetics of the unfolding of alpha-lactalbumin by guanidine hydrochloride (II). The reversible unfolding of alpha-lactalbumin by guanidine hydrochloride, was studied at 25.0 degrees C in a relatively low concentration range of the denaturant (0.80-2.00 mol/l) by means of difference spectra and pH-jump measurements.
|
25b21423-8e25-490d-a875-6bc16acc0055
| 1 |
The unfolding was shown to occur between two states, N and D, because apparent rate-constants of the unfolding and the refolding reactions depended only on pH. All curves plotted as the logarithmical equilibrium constant log KD against pH could fall on the same base curve by shifting each curve along the log KD axis.
|
25b21423-8e25-490d-a875-6bc16acc0055
| 2 |
From the dependence of the logarithmic rate constant on pH, master curves could also be made for the forward and the backward reactions. The dependence of these master curves on pH indicates that the groups affecting the pH dependence of the unfolding are three residues with pKN = 3.3
|
25b21423-8e25-490d-a875-6bc16acc0055
| 3 |
and pKA = pKD = 4.4, one residue with pKN = pKA = 3.8 and pKD = 4.4, and one residue with pKN = 5.8 and pKA = pKD = 6.3, where A indicates the activated state. On the other hand, from the denaturant activity dependence of the shift factors required for making the master curves, the value of the intrinsic binding constant of the denaturant to the protein was found to be similar to that obtained from previous measurements at pH 5.5
|
25b21423-8e25-490d-a875-6bc16acc0055
| 4 |
. Differences between the numbers of the binding sites of the denaturant on the denaturated and the native proteins, and between those on the activated and the native proteins were shown to be 5.3 and 2.1, respectively. The free energy of stabilization in the native-like environment also shows that the protein in the native state is more unstable than lysozyme.
|
697be22c-2bcd-41d5-90ea-049ee358151f
| 0 |
Fluorimetric studies of tryptophyl exposure in concanavalin A. Studies of the iodide ion quenching of the intrinsic fluorescence of Concanavalin A indicate that 50% of the tryptophyl fluorescence originates from exposed residues. This agrees with the X-ray crystallographic determination that two of the four tryptophan residues in a Concanavalin A monomer are on the surface.
|
697be22c-2bcd-41d5-90ea-049ee358151f
| 1 |
Previous studies have indicated that conformational changes induced by sugar binding alter the environment of aromatic residues. The present investigation finds that neither the specific binding of alpha-methyl-D-mannoside nor alteration of the Concanavalin A quaternary structure changes the number or accessibility of the solvent-exposed tryptophan residues.
|
697be22c-2bcd-41d5-90ea-049ee358151f
| 2 |
It therefore appears that the major conformational transitions in Concanavalin A do not affect steric access to the surface tryptophans and the effects previously observed may be ascribed to structurally internal tryptophan residues.
|
cda396a5-cde9-44b8-85d6-df03e65ac306
| 0 |
A study of Folch-Pi apoprotein. II. Relation between polymerization state and conformation. A comparison of the conformation of Folch-Pi apoprotein in organic solvent and in aqueous solutions has been made by ESR, infrared and circular dichroism spectroscopy studies. Electrophoresis and ultracentrifugation have been carried out in order to correlate molecular weight and charge of the molecule with its conformation.
|
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.