UMLS:C0027960 - FACTA Search

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Query: UMLS:C0027960 (mole)
21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Leucine has been found to bind competitively to a soluble protein (molecular weight 97,000 daltons) from rat sciatic nerve under certain experimental conditions to form a high molecular weight aggregate (MW greater than 302,000). Kinetic study showed that the equilibrium constant for leucine-binding is 1.33 X 10(4) l/m and the rate constants for binding and unbinding are k1 = 0.424 l/m/sec and k-1 = 3.18 X 10(5) sec-1 respectively. The binding reaction is accompanied by an endothermic enthalpy change of 5,000 cal/mole and the favorable equilibrium appears to be due to the large positive (35.3 eu) entropy of binding. L-Proline, thymidine, and succinic acid were also found to bind, non-competitively with leucine, to proteins in the same fraction. Binding of those compounds and leucine was enhanced by the presence of Mg2+. Rat muscle and plasma proteins did not significantly bind leucine under these experimental conditions. The presence of this binding protein in rat nerve suggests an additional mechanism in the metabolism and in the transport of amino acids for incorporation into a protein structure in nerve.
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PMID:A binding protein from rat nerve. 59 90

The binding of adenosine diphosphate-ribosylated elongation factor 2 (ADPRib-EF-2) to ribosomes was inhibited both in the presence and absence of GTP in proportion to the amounts of unmodified EF-2 added. Concomitant with this inhibition, an increase in the activity of ribosome-bound EF-2 in polyphenylalanine synthesis was observed. On the other hand, the addition of ADPRib-EF-2 reduced the rate of poly(Phe) synthesis observed in the presence of a saturating amount of EF-2 and increased the amount of EF-2 required for the half-maximal rate of poly(Phe) synthesis. Phe-tRNA, nonenzymatically bound to the ribosome in the presence of poly(U), inhibited the subsequent binding of ADPHRib-EF-2. The same ribosomal population appeared to preferentially bind either aminoacyl-tRNA or ADPRib-EF-2. The Scatchard plot of the binding of ADPRib-EF-2 to the ribosome in the presence of GTP revealed the presence of two ribosomal binding sites (or ribosomal populations) with apparent different affinities for the modified factor (K371 degrees d,1 = 6.6 nM and K37 degrees d,2 = 126 nM). At saturating concentrations of ADPRib-EF-2, a maximum of about 1 molecule of the factor was bound per ribosome. The binding of ADPRib-EF-2 to the ribosome was stimulated by GTP. The binding of radioactive GTP to the ribosome was observed concomitantly with the binding of ADPRib-EF-2. One mole of GTP was bound per mole of ADPRib-EF-2. No significant difference could be found in the binding of GTP to ribosome required in the presence of either EF-2 or ADPRib-EF-2. The binding of ADPRib-EF-2 to the ribosome required the presence of Mg2+ and reached a maximum at 5 mM. The binding was greatest at K+ concentrations below 20 mM. ADPRib-EF-2 was bound primarily to the large ribosomal subunit. A slight, but reproducible binding to the 40 S subunit was also observed. The addition of 40 S to 60 S subunits stimulated the binding of ADPRib-EF-2. GTP displayed a stimulatory effect on the binding only in the presence of recombined subunits. Human ADPRib-EF-2 was bound to rat liver ribosomes as efficiently as to human tonsil ribosomes, while the binding to Escherichia coli ribosomes was insignificant.
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PMID:Interactions of adenosine diphosphate-ribosylated elongation factor 2 with ribosomes. 78 67

D-Ribulose-1,5-bisphosphate (RuBP) carboxylase has been purified from glutamate-CO2-S2O3(2)-grown Thiobacillus intermedius by pelleting the enzyme from the high-speed supernatant and by intermediary crystallization followed by sedimentation into a discontinuous 0.2 to 0.8 M sucrose gradient. The enzyme was homogeneous by the criteria of electrophoresis on polyacrylamide gels of several acrylamide concentrations, sedimentation velocity and equilibrium measurements, and electron microscopic observations of negatively stained preparations. The molecular weights of the enzyme determined by sedimentation equilibrium and light-scattering measurements averaged 462,500 +/- 13,000. The enzyme consisted of closely similar or identical polypeptide chains of a molecular weight of 54,500 +/- 5,450 determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The S(0)20,w of the enzyme was 18.07S +/- 0.22. Electron microscopic examination suggested that the octomeric enzyme (inferred from the molecular measurements mentioned) had a cubical structure. The specific activity of the enzyme was 2.76 mumol of RuBP-dependent CO2 fixed/min per mg of protein (at pH 8 and 30 C), and the turnover number in terms of moles of CO2 fixed per mole of catalytic site per second was 2.6. The enzyme was stable for 3 months at -20 C and at least 4 weeks at 0 C. The apparent Km for CO2 was 0.75 mM, and Km values for RuBP and Mg2+ were 0.076 and 3.6 mM, respectively. Dialyzed enzyme could be fully reactivated by the addition of 20 mM Mg2+ and partially reactivated by 20 mM Co2+, but Cd2+, Mn2+, Ca2+, and Zn2+ had no effect. The compound 6-phosphogluconate was a linear competitive inhibitor with respect to RuBP when it had been preincubated with enzyme, Mg2+, and HCO3-.
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PMID:Purification, quaternary structure, composition, and properties of D-ribulose-1,5-bisphosphate carboxylase from Thiobacillus intermedius. 81 23

The acetylation of spinach ferredoxin by acetic anhydride modified about four moles of amino groups. The absorption spectra, CD spectra, the fluorescence of sole tryptophan residue and the biological activity of acetylated ferredoxin were investigated. An equilibrium existed between two different states, D- and N-form, of the acetylated ferredoxin and was dependent on the cation concentration. D-form completely reverted to N-form upon the binding of one mole of cation, Na+ or Mg2+. Although the N-form was indistinguishable from native ferredoxin in every property tested, the D-form was significantly different from the N-form or native ferredoxin and was very unstable, especially at low salt concentrations. It is suggested that the amino groups might be important in maintaining the protein conformation by forming salt linkages, but may not be essential for the activity. Furthermore, since the D-form, unlike the N-form and native ferredoxin, was inactive in the ferredoxin-NADP+ reductase [EC 1.6.7.1] assay system and had no inhibitory effect in this system, it was considered to be incapable of forming a complex with ferredoxin-NADP+ reductase. On the other hand, the N-form of the modified ferredoxin was as active as native ferredoxin. It is suggested that amino groups of spinach ferredoxin are not essential for the redox reaction of ferredoxin or for complex formation with the reductase.
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PMID:Chemical modification of spinach ferredoxin. Properties of acetylated spinach ferredoxin. 84 28

The complexation of a series of aromatic and alicyclic N,N,N',N'-tetra-n-propyl amides of 1,2-ethylenedioxydiacetic acids with group IIA metal-ion bromides in anhydrous methanol was investigated by ultraviolet absorption spectroscopy. These synthetic ligands were previously found to show selectivity toward divalent over monovalent cations with respect to extraction of ions into bulk organic phase (Borowitz, I.J., Lin, W-O., Wun, T-C., Bittman, R., Weiss, L., Diakiw, V., and Borowitz, G.B. (1977), Tetrahedron, in press). At low concentrations, ligands bearing benzene and naphthalene rings form 1:1 ligand to divalent cation complexes with each of the alkaline-earth metals, but ligands in the cyclohexyl series are stoichiometrically bound to cations in more than one type of complex. Binding isotherms obtained by Scatchard analysis and by the method of continuous variation revealed ligand to divalent ion mole ratios of 2:1, 3:2, and 4:3 for binding of N,N,N',N'-tetra-n-propyl-cis-1,2-cyclohexanedioxydiacetamide with Ca2+, Sr2+, and Ba2+, respectively. In contrast, Scatchard analysis of ultraviolet spectral changes showed that a 1:1 complex is formed between this ligand and Na+ with an apparent association constant of 56 +/- 2M-1; the constant for binding with K+ was smaller (11 M-1). The order of apparent association equilibrium constants for complexation of group IIA cations with this series of neutral ligands was Ca2+ greater than Sr2+ greater than Ba2+ greater than Mg2+; for example, for N,N,N',N'-tetra-n-propyl-1,2-phenylenedioxydiacetamide the apparent binding constants at 25 degrees C were 7.33 +/- 0.25 X 10(4) M-1 for Ca2+, 1.23 +/- 0.03 X 10(4) for Sr2+, 4.42 +/- 0.09 X 10(3) for Ba2+, and 4.04 +/- 0.24 X 10(2) for Mg2+. The divalent cation binding properties of these synthetic diamide ligands are discussed in relation to those of other synthetic ligands and of two naturally occurring ligands.
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PMID:Binding properties of neutral diamide ligands for alkaline-earth cations. 86 Nov 97

The interaction of diethylpyrocarbonate (DEP) with the pyruvate dehydrogenase component (PDH) isolated from the pyruvate dehydrogenase complex (EC 1.2.4.1) results in a modification of 3-5 histidine residues per mole of enzyme, which simultaneously decreases the enzyme activity. After PDH inhibilion by DEP in the presence of dithiothreitol almost complete reactivation (94%) under the effect of neutral hydroxylamine is observed. In the absence of SH-groups protection incomplete reactivation by hydroxylamine (79%) is found. In the latter case titration with 5,5-dithio--bis-(2-nitrobenzoic acid) in 8 M urea showed that the DEP-modified protein contains less quantity of SH groups (by 4-8) as compared to the native enzyme. It is assumed that the DEP-modified SH-groups are not responsible for the enzyme activity. The differential spectrum of the modified and native PDH showed no changes within the range of 260-300 nm. TPP in combination with Mg2+ (10(-3) M) protectes PDH from being inactivated by DEP. TPP (10(-2) M) reactivates PDH by 70% after its complete inhibition by DEP. Similar protective action is manifested by ATP, ADP and inorganic pyrophosphate in the presence of Mg2+. A kinetic study showed a competitive type of PDH inhibition by DEP with respect to TPP. it is concluded that the histidine residues of PDH are involved in TPP binding.
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PMID:[Role of muscle pyruvate dehydrogenase histidine residues in thiamine pyrophosphate binding]. 98 22

The effect of Mg2+ on the binding of adenylates to isolated chloroplast coupling factor 1 (CF1) was studied using CD spectrometry and ultrafiltration. At adenylate concentrations smaller than 100 muM, one mole of CF1 binds three moles of ATP (or ADP) regardless of the presence of Mg2+. In the presence of Mg2+, the first two ATP's bind to CF1 independently with the same binding constant of 2.5 X 10(-1) muM-1, then the third ATP binds with a much higher affinity of 10 muM-1. In the absence of Mg2+, the first ATP binds to CF1 with a binding constant of 2.5 X 10(-1) muM-1 then the other two ATP's bind less easily with the same binding constant of 4.0 X 10(-2) muM-1. The binding mode of ADP to CF1 is quite similar to that of ATP. In the presence of Mg2+, the binding constants of the first two ADP's are both 7.6 X 10(-2) muM-1, that of the third ADP being 4.0 muM-1. In the absence of Mg2+, the binding constant of the first ADP is 7.6 X 10(-2) muM-1, the constants of the other two ADP's both being 4.0 X 10(-2) muM-1. AMP caused a negligible change in CD.
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PMID:Magnesium ion-induced changes in the binding mode of adenylates to chloroplast coupling factor 1. 100 84

Dimethylsulfoxide-water-Dowex 50W-X8 systems are characterized by measurements of solvent selectively and proton magnetic resonance spectra. The H+-, Li+-, NH4+-, NHe4+-, NBu4+-, Mg2+-, Zn2+-, and La3+- forms are studied over a wide range of binary-solvent mole fractions. The relative selectivities for water by the ion exchanger, based on an integrated Kipling parameter, are Zn2+-form (reference) --1.00, Mg2+ --0.43, La3+ --0.38, Li+ +0.17, NMe4+ 0.20, NH4+ 0.31, NBU4+ 0.33, and H+ 0.68, the polyvalent counterions preferring DMSO. All of the ionic forms except the NH4+-form exhibit over much of the mole fraction range separations between the external water and the internal water peaks exceeding 50 Hz, the magnitude of the separation varying with the counter-ion. Comparison of results is facilitated by maintaining a constant ratio between the total number of moles of solvent and the number of equivalents of ions exchanger.
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PMID:Models for biological ion exchangers. II. Solvent selectivity in DMSO-water-Dowex 50W. 102 18

Complexes between tRNAPhe (yeast), tRNASer (yeast) and tRNATyr (Escherichia coli) and their cognate aminoacyl-tRNA synthetases have been studied by sedimentation velocity runs in an analytical ultracentrifuge. The amount of complex formation was determined by the absorption and the sedimentation coefficients of the fast-moving boundary in the presence of excess tRNA or excess synthetase respectively. The same method has been applied to unspecific combinations of tRNAs and synthetases. Inactive material of tRNA or synthetase does not influence the results. 1. Two moles of tRNAPhe can be bound to one mole of phenylalanyl-tRNA synthetase with a binding constant greater than 10(6) M-1. The binding constants for both tRNAs are very similar; the binding sites are independent of each other. Omission of Mg2+ does not prevent binding. 2. Two moles of tRNASer can be bound to one mole of Seryl-tRNA synthetase; the binding of the first and second tRNA is non-equivalent, K1 greater than 10(6) M-1, K2 is determined to be 1.3 X 10(5) M-1 at pH 7.2. Omission of Mg2+ prevents complex formation. 3. Tyrosyl-tRNA synthetase behaves very similarly to seryl-tRNA synthetase. The binding constant for the weakly bound tRNA is 2.3 X 10(5) M-1 at pH 7.2, and 2.5 X 10(6) M-1 at pH 6.0. No complexes are observed in the absence of Mg2+. 4. Unspecific binding was only obtained with phenylalanyl-tRNA synthetase. It binds tRNASer (yeast), tRNAAla (yeast) and tRNATyr (E. coli) with a binding constant about 100 times lower compared to its cognate tRNA. The binding data are discussed with respect to the tertiary structure of the tRNAs, the subunit structure of the synthetases and the possible physical basis for the non-equivalence of binding sites.
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PMID:Equivalent and non-equivalent binding sites for tRNA on aminoacyl-tRNA synthetases. 110 Mar 84

1. A procedure has been described for the purification of the major isozyme of yeast phosphoglucomutase of highest known specific activity. 2. The native enzyme has a molecular weight of about 65400 and was found to be homogeneous as judged by sucrose density gradient centrifugation, gel filtration, electrophoresis on acrylamide gel and ultracentrifugal analysis. In the presence of denaturing agents such as guanidine hydrochloride or sodium dodecyl sulfate, the enzyme dissociated into 32000-molecular-weight subunits. 3. As isolated, the enzyme has one mole of phosphate bound per mole of enzyme. Preparations incubated with 1.0 mM EDTA in 10 mM citrate buffer, pH 5.5 and dialysed against 10 mM metal-free citrate buffer, pH 5.5, contain no intrinsically bound Zn2+ and were enzymically inactive but fully active in the presence of 5 mM Mg2+ and 84% as active with 0.5 mM Zn2+. Simultaneous presence of both ions at these concentrations did not enhance activity. Enzyme was completely and irreversibly inactivated by preincubation with Be2+. Inactive enzyme had one mole of Be2+ bound per mole of enzyme. 4. Enzyme exhibited "ping-pong" kinetics rather than "random sequential". Km values for glucose 1-phosphate and for glucose 1,6-bisphosphate were calculated to be 2.34 times 10(-5) M and 2.24 times 10(-6) M, respectively. Rate of enzyme phosphate turnover was studied with rapid-mixing technique. The rates of 32P release from 32P-labeled enzyme and its appearance as glucose 6-[32P]phosphate were comparable and remained unaffected by addition of glucose 1,6-bisphosphate.
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PMID:Purification and properties of phosphoglucomutase from Fleischmann's yeast. 110 Mar 98

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