Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P17174 (aspartate aminotransferase)
 14,872 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In aspartate aminotransferase (AspAT), His143 is located within a hydrogen-bonding distance to Asp222 that forms a strong ion pair with the ring nitrogen of the coenzyme, pyridoxal 5'-phosphate (PLP) or pyridoxamine 5'-phosphate (PMP). His143 of Escherichia coli AspAT was replaced by Ala or Asn. The mutant enzyme H143A showed a slight increase in the maximum velocity of the overall transamination reaction between aspartate and 2-oxoglutarate, while H143N AspAT showed a decrease to 60% in the maximum rate of the overall reactions in both directions. In all of the half-transamination reactions with four substrates, aspartate, glutamate, oxalacetate, and 2-oxoglutarate, the catalytic competence as defined by kmax/Kd decreased by 3-18-fold upon replacing His143 by either Ala or Asn. The extent of the decrease varied from one substrate to another; it was largely contributed to by the decrease in affinities for all substrates. The equilibrium constants, [PMP-form] [keto acid]/[( PLP-form] [amino acid]), decreased by over 10-fold upon the mutations at position 143. Both H143A and H143N AspATs exhibited a considerably decreased affinity for 2-methylaspartate, an external-aldimine-forming substrate analogue, yet without appreciable alteration in the affinity for succinate and glutarate, which are non-aldimine-forming analogues. All these findings suggest that, although His143 is not essential for catalysis, it might assist the formation of enzyme-substrate complex.
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PMID:The role of His143 in the catalytic mechanism of Escherichia coli aspartate aminotransferase. 200 66

Tryptophanase (tryptophan: indole-lyase) from Escherichia coli has been isolated in the holoenzyme form and its absorption spectra and acid-base chemistry have been reevaluated. Apoenzyme has been prepared by dialysis against sodium phosphate and L-alanine and molar absorptivities of the coenzyme bands have been estimated by readdition of pyridoxal 5'-phosphate. The spectrophotometric titration curve, whose midpoint is at pH 7.6 in 0.1 M potassium phosphate buffers, indicates some degree of cooperativity in dissociation of a pair of protons. Resolution of the computed spectra of individual ionic forms of the enzyme with lognormal distribution curves shows that band shapes are similar to those of model Schiff bases and of aspartate aminotransferase. Using molar areas from the latter we estimated amounts of individual tautomeric species. In addition to ketoenamine and enolimine or covalent adduct the high pH form also appears to contain approximately 18% of a species with a dipolar ionic ring (protonated on the ring nitrogen and with phenolate -O-). We suggest that this may be the catalytically active form of the coenzyme in tryptophanase. The equilibrium between tryptophanase and L-alanine has also been reevaluated.
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PMID:Equilibria and absorption spectra of tryptophanase. 203 39

The complete amino acid sequence of rat liver cytosolic alanine aminotransferase (EC 2.6.1.2) is presented. Two primary sets of overlapping fragments were obtained by cleavage of the pyridylethylated protein at methionyl and lysyl bonds with cyanogen bromide and Achromobacter protease I, respectively. The protein was found to be acetylated at the amino terminus and contained 495 amino acid residues. The molecular weight of the subunit was calculated to be 55,018 which was in good agreement with a molecular weight of 55,000 determined by SDS-PAGE and also indicated that the active enzyme with a molecular weight of 114,000 was a homodimer composed of two identical subunits. No highly homologous sequence was found in protein sequence databases except for a 20-residue sequence around the pyridoxal 5'-phosphate binding site of the pig heart enzyme [Tanase, S., Kojima, H., & Morino, Y. (1979) Biochemistry 18, 3002-3007], which was almost identical with that of residues 303-322 of the rat liver enzyme. In spite of rather low homology scores, rat alanine aminotransferase is clearly homologous to those of other aminotransferases from the same species, e.g., cytosolic tyrosine aminotransferase (24.7% identity), cytosolic aspartate aminotransferase (17.0%), and mitochondrial aspartate aminotransferase (16.0%). Most of the crucial amino acid residues hydrogen-bonding to pyridoxal 5'-phosphate identified in aspartate aminotransferase by X-ray crystallography are conserved in alanine aminotransferase. This suggests that the topology of secondary structures characteristic in the large domain of other alpha-aminotransferases with known tertiary structure may also be conserved in alanine aminotransferase.
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PMID:Complete amino acid sequence of rat liver cytosolic alanine aminotransferase. 204 42

The vitamin B-6 requirements of 12 men and women over 60 y old were studied. The protocol consisted of a 5-d baseline period and four experimental periods during which the subjects successively received 0.003, 0.015, 0.0225 and 0.03375 mg of vitamin B-6/(kg body wt.d). Dietary protein was 1.2 or 0.8 g/(kg body wt.d). At 5- or 6-d intervals, xanthurenic acid (XA) after a 5-g L-tryptophan load and 4-pyridoxic acid (4-PA) in 24-h urine, erythrocyte aspartate aminotransferase activity coefficient (EAST-AC) and plasma pyridoxal-5'-phosphate (PLP) were measured. These measurements were abnormal during vitamin B-6 depletion but returned to normal during repletion. Men who ingested approximately 120 g protein/d required 1.96 +/- 0.11 mg of vitamin B-6 to normalize XA; women who ingested 78 g protein/d required 1.90 +/- 0.18 mg of vitamin B-6 to normalize XA. To attain normal levels of EAST-AC and 4-PA in men, 2.88 +/- 0.17 mg of vitamin B-6 were needed; to normalize PLP, 1.96 +/- 0.11 mg of vitamin B-6 were required. Women required 1.90 +/- 0.18 mg or more of vitamin B-6 to normalize these measurements. Vitamin B-6 requirements were not decreased in two of three subjects who ingested 54 g of protein daily. Thus, vitamin B-6 requirements of elderly men and women are about 1.96 and 1.90 mg/d, respectively.
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PMID:Vitamin B-6 requirements of elderly men and women. 205 Dec 26

Forty-five male Lohmann chicks were grown up to 6 weeks of age. The experimental diet containing a high protein level (30%) was aimed at increasing the metabolic need for PN. Microbiological analysis on the basal ration revealed a marginal content of 4.7 mumol PN/kg. The vitamin B6 status was assessed at the end of the experiment according to the basal activity of aspartate aminotransferase (AspAT) in plasma and in erythrocytes, and the in vitro stimulated activity with pyridoxal 5'-phosphate (PLP). None of the deficient chicks had any clinical signs attributable to malfunction of the nervous system, and they grew as well as those receiving the control diet. Vitamin B6 deficiency was biochemically confirmed by a significant depression of AspAT activity in plasma (p less than 0.001) and in erythrocytes (p less than 0.01). The addition of PLP in vitro enhanced the catalytic activity of the plasma enzyme, but had negligible effect on the erythrocyte enzyme. The degree of stimulation in vitro of the apoenzyme of AspAT not only depends on the endogenous vitamin B6 content, but also on the basal activity of the enzyme. A 15-day repletion period with a daily oral dose (50 mumol PN) did not result in a complete restoration of the enzyme activity, indicating that the availability of apoenzyme had been curtailed. This experiment demonstrated that chicks fed a high protein corn-soyamin diet with a limited amount of PN but containing Saccharomyces yeast showed no nervous signs or perosis, but significant metabolic disturbances.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Aspartate aminotransferase activity in experimentally induced asymptomatic vitamin B6 deficiency in chicks. 205 99

The active site residue lysine 258 of chicken mitochondrial aspartate aminotransferase was replaced with a histidine residue by means of site-directed mutagenesis. The mutant protein was expressed in Escherichia coli and purified to homogeneity. Addition of 2-oxoglutarate to its pyridoxamine form changed the coenzyme absorption spectrum (lambda max = 330 nm) to that of the pyridoxal form (lambda max = 330/392 nm). The rate of this half-reaction of transamination (kcat = 4.0 x 10(-4)s-1) is five orders of magnitude slower than that of the wild-type enzyme. However, the reverse half-reaction, initiated by addition of aspartate or glutamate to the pyridoxal form of the mutant enzyme, is only three orders of magnitude slower than that of the wild-type enzyme, kmax of the observable rate-limiting elementary step, i.e. the conversion of the external aldimine to the pyridoxamine form, being 7.0 x 10(-2)s-1. Aspartate aminotransferase (Lys258----His) thus represents a pyridoxal-5'-phosphate-dependent enzyme with significant catalytic competence without an active site lysine residue. Apparently, covalent binding of the coenzyme, i.e. the internal aldimine linkage, is not essential for the enzymic transamination reaction, and a histidine residue can to some extent substitute for lysine 258 which is assumed to act as proton donor/acceptor in the aldimine-ketimine tautomerization.
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PMID:Aspartate aminotransferase with the pyridoxal-5'-phosphate-binding lysine residue replaced by histidine retains partial catalytic competence. 210 17

The erythrocyte aspartate aminotransferase and renal and intestinal glycogen phosphorylase activities in rats are determined as dependent on their provision with vitamin B6. It has been shown that the aspartate aminotransferase activity decreases and the shape of the aspartate concentration-activity curve changes in the vitamin B6-deficient animals. The B6 insufficiency does not affect the intestinal mucosa glycogen phosphorylase. However the renal phosphorylase activity decreases by 30 percent in the vitamin B6 deficient rats. It occurs due to changes in the affinity of phosphorylase A and B to glucose-1-phosphate but not to AMP. The activation of these investigated enzymes by exogenous pyridoxal phosphate reveals no essential differences between the vitamin B6-deficient and normal rats. The possible causes of the observed changes in the aspartate aminotransferase and phosphorylase activity are discussed.
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PMID:[Changes in kinetic properties of pyridoxal-dependent enzymes during dietary vitamin B6 deficiency in rats]. 211 Jun 92

The structure of Escherichia coli aspartate aminotransferase complex with the inhibitor 2-methylaspartate, and that of the mutant enzyme in which an arginine was substituted for a lysine residue thereby forming a Schiff base with the coenzyme pyridoxal 5'-phosphate, were determined at 2.5 A resolution, by the molecular replacement method using the known structure of pig cytosolic aspartate aminotransferase. The enzyme catalyzes the reversible transamination between L-aspartate and alpha-ketoglutarate, and forms a dimeric structure of two identical subunits. Each subunit comprises two domains, a small and a large one. Although, in general, the overall and secondary structure of E. coli enzyme are similar to those of higher animals, some differences of enzymatic action between the enzyme from E. coli and those from higher animals could be explained on the basis of the X-ray structures and molecular mechanics calculation based on them.
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PMID:Three-dimensional structures of aspartate aminotransferase from Escherichia coli and its mutant enzyme at 2.5 A resolution. 212 25

Following acute accidental death of 26 cows exposed to boron fertilizer, effects of inorganic boron treatment in goats were studied. Goats were orally dosed with toxic but sublethal amounts of the fertilizer. Multiple hematologic and serum chemistry parameters were assessed, as were cerebrospinal fluid (CSF) neurotransmitters and some of their metabolites. Significant increases in packed cell volume, hemoglobin, inorganic phosphate, creatine phosphokinase, conjugated bilirubin, sodium, glucose, cholesterol, and aspartate transaminase were recorded. The following serum components were significantly decreased after boron dosing: alkaline phosphatase, magnesium, glutamyltransferase and potassium. There was evidence of a stimulatory effect on both serotonergic and dopaminergic neurons as reflected in elevated CSF monoamine metabolites. Aberrations in clinical behavior, including seizure-like activity, also suggested a central nervous system effect of inorganic boron.
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PMID:Experimental acute inorganic boron toxicosis in the goat: effects on serum chemistry and CSF biogenic amines. 216 93

To obtain more insight into the effect of dietary fiber on vitamin B6 status among elderly people, we studied dietary interrelationships as well as associations between dietary intake and plasma pyridoxal-5'-phosphate (PLP) and cofactor stimulation of aspartate aminotransferase in erythrocytes (EAST-AC) among 441 nonvegetarian (aged 65-79) and 32 vegetarian elderly (aged 65-94). EAST-AC was found to be inversely related with intake of vitamin B6 and dietary fiber in bivariate regression analyses. After adjustment for age, intake of energy, protein, and fiber, the intake of vitamin B6 was still inversely related with EAST-AC. The association between EAST-AC and dietary fiber disappeared in the multivariate analysis, whereas total protein intake proved to be positively related with EAST-AC in the multivariate analysis only. The differences between bi- and multivariate analyses are most likely due to the observed interrelationships between intake of vitamin B6, fiber, and protein. It is concluded that dietary fiber does not have a significant impact on the vitamin B6 status among Dutch elderly people, since only protein (positively) and vitamin B6 (inversely) intake appeared to be related with EAST-AC in the multivariate analysis.
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PMID:Effect of dietary fiber on the vitamin B6 status among vegetarian and nonvegetarian elderly (Dutch nutrition surveillance system). 216 68


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