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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Imidazole catalysis of phenylalanyl transfer from phenylalanine adenylate anhydride to the hydroxyl groups of homopolyribonucleotides was investigated as a chemical model of the biochemical aminoacylation of tRNA. Imidazole catalyzed transfer of phenylalanine to poly(U) increases from pH 6.5 to 7.7 and decreases above pH 7.7. At pH 7.7 approximately 10% of the phenylalanyl residues are transferred to poly(U). At pH 7.1, transfer to poly(U) was five times as great as to poly(A) and transfer to a poly(A) poly(U) double helix was negligible. At pH 7.1 approximately 45 mole percent linkages to poly(U) were monomeric phenylalanine; the remainder of the linkages were peptides of phenylalanine. The number of linkages and their lability to base and neutral hydroxylamine indicates that phenylalanine and its peptides are attached as esters to the 2' hydroxyl groups throughout poly(U) and the 2' (3') hydroxyl groups at the terminus of poly(U). These results do model the contemporary process of aminoacyl transfer to tRNA and continue to suggest that a histidine residue is in the active site of aminoacyl-tRNA-synthetases.
J Mol Evol 1975 Dec 29
PMID:Aminoacyl transfer from an adenylate anhydride to polyribonucleotides. 0 44

The effect of anions Cl- and I- on structural and kinetic properties of LDH was investigated. It was shown that anions are specific inhibitors of LDH competing with pyruvate in the active ternary complex, LDHNADHpyq. The following dissociation constants for the anions were obtained from inhibition data: 0.4 +/- 0.02 and 0.07 +/- 0.01 M for Cl- and I-, respectively. The slope of Hill plot are near 1.0. The anions abolished the inhibition of LDH at high pyruvate concentrations. The following dissociation constants were obtained from these data: 0.1 and 0.015 M for Cl- and I- respectively. The inhibition by anions and the abolishing of substrate inhibition by anions were studied also for the lactate oxidation reaction. The dissociation constants for anions obtained from these data are in good correlation with the constants obtained for the pyruvate reduction reaction. It was concluded that anions do not interact with the group at the catalytic site with pK approximately 7.8, presumably His-195. The degree of pyruvate inhibition does not depend on the buffer system. The differences in the degree of inhibition obtained previously in phosphate, imidazole and tris-buffer systems can be explained by the presence of Cl- anions in the last two buffer. The rate constants of hydroxy leads to keto pyruvate transition was obtained in various buffer systems. It was shown that the hydroxy-form of pyruvate does not cause the inhibition of LDH.
Mol Biol (Mosk)
PMID:[Effect of anions on inhibition of lactate dehydrogenase by pyruvate]. 2 75

Reversible unfolding of bovine chymotrypsinogen A in 2H2O either by heating at low pH or by exposure to 6 M guanidinium chloride results in the exchange of virtually all the nitrogen-bound hydrogens that give rise to low-field 1H NMR peaks, without significant exchange of the histidyl ring Cepsilon1 hydrogens. These preexchange procedures have enabled the resolution of two peaks, using 250-MHz correlation 1H NMR spectroscopy, that are attributed to the two histidyl residues of chymotrypsinogen A. Assignments of the Cepsilon1 hydrogen peaks to histidine-40 and -57 were based on comparison of the NMR titration curves of the native zymogen with those of the diisopropylphosphoryl derivative. Two histidyl Cepsilon1 H peaks were also resolved with solutions of preexchanged chymotrypsin Aalpha. The histidyl peaks of chymotrypsin Aalpha were assigned by comparison of NMR titration curves of the free enzyme with those of its complex with bovine pancreatic trypsin inhibitor (Kunitz). The NMR titration curves of histidine-57 in the zymogen and enzyme and histidine-40 in the zymogen exhibit two inflections; the additional inflections were assigned to interactions with neighboring carboxyl groups: aspartate-102 in the case of histidine-57 and aspartate-194 in the case of histidine-40 of the zymogen. In bovine chymotrypsinogen A in 2H2O at 31 degrees C, histidine-57 has a pK' of 7.3 and aspartate-102 a pK' of 1.4, and the histidine-40-aspartate-194 system exhibits inflections at pH 4.6 and 2.3. In bovine chymotrypsin Aalpha under the same conditions, the histidine-57-aspartate-102 system has pK' values of 6.1 and 2.8, and histidine-40 has a pK' of 7.2. The results suggest that the pK' of histidine-57 is higher than the pK' of aspartate-102 in both zymogen and enzyme. A significant difference exists in the structure and properties of the catalytic center between the zymogen and activated enzyme. In addition to the difference in pK' values, the chemical shift of histidine-57, which is highly abnormal in the zymogen (deshielded by 0.6 ppm), becomes normalized upon activation. These changes may explain part of the increase in the catalytic activity upon activation. The 1H NMR chemical shift of the Cepsilon1 H of histidine-57 in the chymotrypsin Aalpha-pancreatic trypsin inhibitor (Kunitz) complex is constant between pH 3 and 9 at a value similar to that of histidine-57 in the porcine trypsin-pancreatic trypsin inhibitor complex [Markley, J.L., and Porubcan, M. A. (1976), J. Mol. Biol. 102, 487--509], suggesting that the mechanisms of interaction are similar in the two complexes.
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PMID:Zymogen activation in serine proteinases. Proton magnetic resonance pH titration studies of the two histidines of bovine chymotrypsinogen A and chymotrypsin Aalpha. 3 98

High protein dietary content stimulates urea formation in ureotelic animals but does not exert almost any effect on ammonia production from L-amino acids in vitro. L-histidine and L-threonine are the only amino acids which are most actively deaminated by ureotelic animals fed on a high protein diet. All the steps of L-histidine metabolism have been studied: it has been found that both the histidine transaminase pathway and the histidase pathway are stimulated. Glutamic acid is also a product of histidine catabolism through the histidase pathway, but its catabolism is unaffected by the dietary protein content. These data suggest the existence of independent mechanism controlling the catabolism of the two amino acids.
Mol Cell Biochem 1979 Jan 26
PMID:Histidine degradation enzymes in rat liver: induction by high protein intake. 3 41

Rose-bengal-sensitized photooxidation of aspartate transaminase from chicken heart cytosol results in a loss of enzymatic activity which follow first order kinetics down to 70--75% inactivation. 0.9 Histidine, 0.9 tryptophane residues and 1.5 SH groups per enzyme subunit were found to be modified in the photooxidized transaminase, which retained 26% residual activity. Photodestruction of the coenzyme was about 16%. The rate of enzyme photoinactivation is constant in the pH range 6--8, and drastically decreases with lowering pH from 6 to 4. alpha-Ketoglutarate partially protects the holoenzyme from inactivation. The apoenzyme undergoes photoinactivation at a rate almost twice as rapid as the holoenzyme. Photooxidized apotransaminase retains affinity to pyridoxal phosphate and binds as much coenzyme as the native apoenzyme. Photooxidation induces no significant alterations in the circular dichroism pattern of the enzyme in the 200 to 240 nm range. However, positive circular dichroism is markedly increased in the absorption bands of aromatic amino acids (260--300 nm). The affinity of photooxidized holoenzyme for glutarate and alpha-methyl aspartate is greatly decreased. On the other hand, photooxidized enzyme retains its ability to bind alpha-alanine and to catalize the transamination half-reaction between alpha-alanine and the bound coenzyme. These findings imply that photooxidation disturbs the binding of the distal carboxyl group of dicarboxylic substrates. This may be due to a localized conformational change induced by destruction of a photoreactive histidine residue at the active site. A role of the histidine residue in transamination reaction is discussed.
Mol Biol (Mosk)
PMID:[Photooxidation of aspartate transaminase from chicken heart cytosol]. 3 52

The pH-dependence of the reduction rate of ferricytochrome C by intact and chemically modified oxymyoglobins has been studied. The modification was performed with respect to histidine residues and alpha-aminogroup of N-terminal valine. Two histidine residues of myoglobin, His A10 and His GH1, are shown to take part in the realization of the "active" contact between the molecules in the course of the reaction. The deprotonation of the first residue contributes to the acceleration and that of the second to the reduction of the reaction. The found orientation of the Mb molecules in the "active complex" implies that at any orientation of cytochrome C the distance between the haemes of the both molecules should be more than 30 A. This makes highly probable that a structure-dependent mechanism of electron transfer in the system under study can be proposed.
Mol Biol (Mosk)
PMID:[Electron transfer to hemoproteins. II. pH-dependence of the reduction rate of ferricytochrome c by oxymyoglobin]. 3 34

A model has been proposed to account for growth inhibition by L-histidine in a variant strain of Nostoc muscorum. This strain has been characterized for its response to 3-amino-1,2,4-triazole and 1,2,4-triazole-3-alanine known to act as false core-pressors of the histidine biosynthesis genes. The histidine sensitive strain retained its sensitivity to triazole alanine while the inhibitory effects of aminotriazole were much reduced indicating a change in regulation of his genes. The probable interactions between nif and his genes in cyanobacteria (blue-green algae) have been discussed.
Mol Gen Genet 1979 Feb 16
PMID:Histidine sensitive variant of the blue-green alga Nostoc muscorum: response to corepressors of histidine biosynthesis. 10 14

Specific modification of the monomeric fraction III of ferri-hemoglobin from insect larvae Chironomus thummi thummi (Hb CTT) was studied on histidyl residues His-G19 (pK 4,8), His-E5 (pK 7,3) and Met-H22 at different pH using iodacetamide and spin label 2,2,6,6-tetramethyl-4-bromacethyl-piperidin-1-oxyl, an analogue of bromacetate. The analysis of the products of carboxymethylation (CM) showed that at pH 5,0 two products of modification CM-(His-G19)-Hb CTT, and CM-(Met-H22)-Hb CTT were obtained. In the case of modification at pH 7,2 with a spin label dicarboxymethylatid product CM-(His-G19)-CM (His-E5)-Hb CTT is obtained. In all products the degree of modification was one spin label per mole protein. Based on the data on the primery and tertiary structures Hb CTT and the results of the investigation, different reactivity of His-G19 and His-E5, as well as the cause of the absence of the product of carboxymethylation on His-G2 have been discussed. By analizing the absorption spectra of carboxymethylated derivatives of hemoglobin in the ultraviolet and visible region, as well as from the pH dependence curves of the absorption at Soret band in the interval pH 5,5-11,5 it has been shown that carboxymethylation of His-G19 and His E5 is not accompanied by any substantial disturbance of the structures of aquous-complexes Hb CTT. Modification of Met-H22 leads to strong changes in the absorption spectrum and to the absence of pH dependence of the absorption at Soret band, which indicates a change in the aquous-complexes Hb CTT structure.
Mol Biol (Mosk)
PMID:[Selected carboxymethylation of ferri-hemoglobin from insect larvae Chironomus thummi thummi]. 17 63

1. A colorimetric method was developed for the direct chemical assay of human carboxypeptidase A (carboxypolypeptidase; EC 3.4.12.2) with angiotensin converting enzyme-like activity in serum or plasma, with the substrate analogue glycyl-L-histidylglycine and the angiotensin converting enzyme substrate angiotensin I (A-I). This method was based on the spectrophototometric determination of histidylglycine and histidyl-leucine, products of the hydrolysis of glycyl-L-histidylglycine and A-I respectively. omicron-Phthalaldehyde reacted with the imidazole moiety of nu-terminal histidyl peptides to produce a yellow chromophore. 2. A large number of inhibitors were tested for their effects on carboxypolpeptidase activity. The hydrolysis of Gly-His-Gly and A-I was inhibited by histidyl-leucine and angiotensin II, both products of the hydrolysis of A-I. Bothrops jararaca venom extract, EDTA, rho-chloromercuribenzoate, 8-hydroxyquinoline and 2,3-dimercaptopropanol, previously reported as converting enzyme inhibitors, also inhibited carboxypolypeptidase activity. 3. Angiotensin converting enzyme activity in the serum of sixty-six adults ranged from 10 to 37 nmol of glycyl-L-histidylglygine hydrolysed in 10 min by 10 mu1 of serum at 37 degrees C and pH 7-25.
Clin Sci Mol Med 1976 May
PMID:The spectrophotometric determination of human serum carboxypolypeptidase with angiotensin converting enzyme-like activity. 17 49

Iodoacetamide, N-ethylmaleimide, p-hydroxymercuribenzoate (p-MB) and HgCl2 were tested as inhibitors of microsomal glucose-6-phosphatase. Iodoacetamide had no effect at 2 mM. N-ethylmaleimide inhibited only crude, but not purified microsomal preparations (M2) or crude microsomes exposed to deoxycholate. 14C-labelled N-ethylmaleimide was not bound by the M2 protein fraction. p-MB inhibited all types of preparations and the inhibition was not counteracted by detergent. A more detailed study was carried out with the purified M2 fraction (specific activity: 2-4 mumoles Pi/min/mg protein). Glucose-6-phosphate hydrolysis was inhibited 50% by 5 X 10(-5) M p-MB. The inhibition was completely reversible by dithiothreitol except when the enzyme was pre-incubated with p-MB in the absence of substrate. Then p-MB accelerated the temperature-dependent inactivation of glucose-6-phosphatase. Binding studies showed that around 3 mumoles 14C-p-MB were incorporated into 100 mg M2 protein regardless of the concentration of mercurial in the incubation mixture. That is, over a 25 fold range of p-MB concentration, causing up to 80% inhibition of enzyme activity, no difference was seen in the amount of labelled p-MB which was irreversibly bound to M2 protein. Kinetically p-MB behaved like a reversible inhibitor and this was confirmed by dilution experiments. Several compounds, including some amino acids, antagonized the inhibition by p-MB. The order of effectiveness was EDTA greater than barbital greater than tryptophan greater than histidine greater than lysine greater than other amino acids. Glycine, Tris and urea were ineffective competitors of p-MB inhibition. Double reciprocal plots showed that the Km for glucose-6-phosphate was increased and the Vmax reduced in the presence of p-MB. HgCl2 was a more effective inhibitor than p-MB with a Ki of 6 X 10(-6) M. We conclude that a reaction of p-MB with M2 sulfhydryls does not play a part in the inhibition of enzyme activity. It is suggested that p-MB may interact with one or more amino acid side chains in such a way that enzyme conformation is altered.
Mol Cell Biochem 1976 Jul 30
PMID:The effect of p-hydroxymercuribenzoate and congeners on microsomal glucose-6-phosphatase. 18 75


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