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PubMed1985

Levels of ornithine aminotransferase messenger RNA under conditions of cyclic AMP induction in cultured hepatocytes.

In primary cultures of adult rat hepatocytes, the relative rate of ornithine aminotransferase synthesis is increased approximately 7- to 8-fold in response to dibutyryl cyclic AMP. The corresponding increase in ornithine aminotransferase messenger RNA under these conditions was observed to be only 2- to 3-fold. The levels of ornithine aminotransferase mRNA were measured by hybridization of cellular RNA to a cloned cDNA probe. The ribosomal transit time (20-25 min) along ornithine aminotransferase mRNA was the same in both control and induced cultures. The level of ornithine aminotransferase nascent chains in cAMP-induced cultures was increased 7-fold over the level in control cultures. In the face of a 2- to 3-fold increase in the amount of ornithine aminotransferase mRNA, this suggests an approximately 3-fold increase in the rate of initiation per copy of ornithine aminotransferase messenger RNA. These results indicate that cAMP may regulate ornithine aminotransferase synthesis at both transcriptional and translational levels in cultured hepatocytes.

Animals↗

PubMed1989

The structure of tyrosine aminotransferase. Evidence for domains involved in catalysis and enzyme turnover.

The primary structure of tyrosine aminotransferase, as deduced from the nucleotide sequence of complementary DNA, was confirmed by fast atom bombardment mass spectrometry of tryptic peptides derived from the purified protein. Limited digestion of the native enzyme with trypsin released an acetylated, amino-terminal peptide; the new amino terminus in the modified enzyme was Val65. Endogenous proteases generated a chromatographically separable form of tyrosine aminotransferase that began at Lys35. Neither trypsin nor the other proteases altered the catalytic activity of tyrosine aminotransferase. Reduction of the holoenzyme with sodium borohydride yielded a major tryptic peptide containing phosphopyridoxamine bound to lysine 280, which probably functions in transamination. The carboxyl terminus of tyrosine aminotransferase contains features that typify proteins with short half-lives; it includes two negatively charged, hydrophilic segments that are enriched for glutamyl residues and are similar to a PEST region in ornithine decarboxylase (Rogers, S., Wells, R., and Rechsteiner, M. (1986) Science 234, 364-368). Tyrosine aminotransferase belongs to a superfamily of enzymes which includes aspartate aminotransferase and can be aligned so that many invariant, functional residues coincide. Like the isoenzymes of aspartate aminotransferase, tyrosine aminotransferase may contain two domains, with a central, catalytic core, and a small domain made up of both amino- and carboxyl-terminal components. We speculate that the exposed small domain may confer the unusually rapid degradative rate that characterizes this enzyme.

Amino Acid Sequence↗

PubMed1988

Persulfide generated from L-cysteine inactivates tyrosine aminotransferase. Requirement for a protein with cysteine oxidase activity and gamma-cystathionase.

Liver cytosols contain factors that produce an inhibitor of tyrosine aminotransferase and other enzymes when incubated with L-cysteine or L-cystine. Cystine-dependent inactivation was caused by cystathionase and required pyridoxal 5'-phosphate, but a second protein was needed to reconstitute cysteine-dependent inactivation. A cytosolic protein was isolated that oxidized free cysteine and brought about inactivation of tyrosine aminotransferase when coincubated with cystathionase. Hematin also oxidized cysteine, which led to cysteine-dependent inactivation of tyrosine aminotransferase in the presence of cystathionase. The inactivation of tyrosine aminotransferase involved three steps: initial oxidation of cysteine to form cystine; desulfuration of cystine catalyzed by cystathionase to form the persulfide, thiocysteine; and reaction of thiocysteine (or products of its decomposition) with proteins to form protein-bound sulfane. Since dithiothreitol reactivated tyrosine aminotransferase, the sulfane probably inactivated the enzyme by oxidation of thiol groups. The present results do not indicate whether the cysteine oxidase activity is enzymatic nor do they prove which form of polysulfide inactivates tyrosine aminotransferase. Reduced glutathione greatly slowed the rates at which sulfane accumulated and at which tyrosine aminotransferase was inactivated. Incubation of DL-cystathionine with liver cytosols led to formation of cysteine, which was oxidized and cleaved to form persulfide, and caused inactivation of tyrosine aminotransferase. Thus, sulfane sulfur that is generated by an enzyme of the transulfuration pathway inactivates a transaminase by nonselective oxidation of enzyme-bound thiol groups.

Animals↗

PubMed1984

Developmental profiles and properties of hepatic peroxisomal apo- and mitochondrial holoalanine:glyoxylate aminotransferase during chick embryogenesis.

Alanine:glyoxylate aminotransferase was present as the apoenzyme in the peroxisomes and as the holoenzyme in the mitochondria in chick embryos. The peroxisomal enzyme predominated in the early stage and gradually decreased during embryonic development and disappeared after hatching. In contrast, the mitochondrial enzyme gradually increased and predominated in the later stage of chick embryos. Peroxisomal alanine:glyoxylate aminotransferase in chick embryos was a single peptide with a molecular weight of about 40,000. The enzyme differed from the mitochondrial enzyme in the embryos, and mammalian alanine:glyoxylate aminotransferases 1 (with a molecular weight of about 80,000 with two identical subunits) and 2 (with a molecular weight of about 200,000 with four identical subunits) in molecular weights and immunological properties. Mitochondrial alanine:glyoxylate aminotransferase in chick embryos had an identical molecular weight and immunologically cross-reacted with mammalian mitochondrial alanine:glyoxylate aminotransferase 2. Pyridoxal 5'-phosphate dissociated easily from the peroxisomal enzyme saturated with pyridoxal 5'-phosphate. Hepatic aspartate:2-oxoglutarate aminotransferase and alanine:2-oxoglutarate aminotransferase in chick embryos, and hepatic alanine:glyoxylate aminotransferases in different animal species were all present as the holoenzyme.

Alanine Transaminase↗

PubMed1999

Clodronate as a cause of aminotransferase elevation.

Adverse events (AEs) associated with bisphosphonates are usually gastrointestinal, but elevation of aminotransferases (alanine and aspartate aminotransferase) has also been described in many cases. The frequency of such elevation is, however, poorly investigated. The Probone study is a continuing phase II trial of 610 osteopenic women randomized for 3 years to receive placebo or clodronate at the following clodronate doses: 65 mg, 400 mg and 800 mg daily, and 400 mg for 15 days out of 90 (intermittent group). During the first study year, gastrointestinal AEs were reported by 20-26% of the patients in the five study groups, but no differences appeared between groups. The high-dose clodronate groups (400 mg and 800 mg daily) had no more hepatic side-effects than the low-dose groups, and no serious AE due to liver disease was reported. These higher doses of clodronate caused, however, a mean alanine aminotransferase (ALT) elevation of 5.4-5.8 U (25-24%) which differed significantly from the change in the placebo group (p = 0.002 and p<0.0001, respectively). In those volunteers with initially normal aminotransferase values the risk ratio for an aminotransferase increase to an above-normal value (compared with the placebo group) during the study year was up to 1.8 in the clodronate 400 mg group and up to 2.5 in the clodronate 800 mg group. Among these groups an elevation above the normal limits occurred in up to 11.7% of the volunteers for aspartate aminotransferase (AST) and up to 17.7% for ALT. The respective percentages in the placebo group were 6.2% and 7. 2%. All analyzed bilirubin values were normal. We conclude that oral clodronate use may elevate serum aminotransferase levels, and that these enzymes most likely come from the liver. This elevation has also been described for several other bisphosphonates. However, clinically significant liver injury is unlikely.

Alanine Transaminase↗

PubMed1984

Relationship between plasma pyridoxal-5'-phosphate concentration and the apoenzyme content of serum aminotransferases in patients with a renal allograft.

In 76 patients with a renal allograft the plasma concentration of pyridoxal-5'-phosphate, the activity concentrations of aspartate aminotransferase and alanine aminotransferase and the percentage stimulation of both enzymes have been investigated. Generally, the concentration of the coenzyme was decreased in the patient group compared to normal individuals. The percentage increase of aspartate aminotransferase is the same for the patients as for the normal group. However, the stimulation of alanine aminotransferase is greatly increased for the patient group except for those patients who received cyclosporine A instead of azathioprine. The highly significant inverse correlation between the plasma pyridoxal-5'-phosphate concentration and the percentage stimulation of the enzymatic activity of aspartate aminotransferase and alanine aminotransferase observed before for a normal group, is not present in our patient group. The percentage increase is independent on the activity concentration of the enzymes. It is concluded that the high stimulation of alanine aminotransferase depends on the administration of azathioprine.

Adult↗

PubMed1987

Apoenzyme content of serum aminotransferases in patients with a renal allograft treated with cyclosporine A and azathioprine.

In 16 patients with a renal allograft the activity concentrations of aspartate aminotransferase and alanine aminotransferase and the percentage stimulation of both enzymes were investigated. After the transplantation the patients received prednisone and cyclosporine A as immunosuppressive therapy, while exactly 3 months after the date of transplantation prednisone and azathioprine were given as immunosuppressives. In the first period, the percentage increase of the activity concentration of aspartate aminotransferase and alanine aminotransferase upon supplementation of pyridoxal-5'-phosphate in vitro were similar to that of healthy individuals. In the second period, however, the percentage increase of the activity concentration of alanine aminotransferase was much higher than that of aspartate aminotransferase. Cyclosporine A given during a period of about 400 days did not influence the percentage increase of both enzymes. It is concluded that the high stimulation of alanine aminotransferase in the second period depends on the presence of azathioprine or its metabolites in serum.

Adult↗

PubMed1990

Proteolytic measurement of mitochondrial aspartate aminotransferase in human serum.

A new proteolytic measurement of serum mitochondrial aspartate aminotransferase was evaluated using cytosolic aspartate aminotransferase inactivating protease. Some of the proteases, such as, alpha-chymotrypsin, subtilisin and cytosolic aspartate aminotransferase inactivating protease 401 from Streptomyces species, also specifically inactivated cytosolic aspartate aminotransferase, but not mitochondrial, aspartate aminotransferase. The protease 401 was the most heat stable for storage and showed a higher inactivation rate for cytosolic aspartate aminotransferase--up to 7000 IU/L--more than 200-fold the upper limit. The coefficient of variation of the proteolytic method was less than 10%. Results by the present method correlated with those by the immunochemical method (r = 0.970) and the regression curve was Y = 0.95X + 1.60 (Y: immunochemical method; X: proteolytic method). In the present assay system, reference values for mitochondrial aspartate aminotransferase activity in 500 healthy people ranged from 2.0-7.2 U/L (mean 3.8 U/L).

Aspartate Aminotransferases↗

PubMed1994

A simple method for determination of stereospecificity of aminotransferases for C-4' hydrogen transfer of the coenzyme.

A simple method was established for determination of the stereospecificity of C-4' hydrogen transfer of the coenzymes (pyridoxal and pyridoxamine). The method is based on the findings that aspartate aminotransferase of pig heart and D-amino acid aminotransferase of Bacillus sp. YM-1 catalyze the abstraction of the pro-S and pro-R proton at C-4' of pyridoxamine, respectively. Pyridoxal is a poor coenzyme, but readily released from the enzyme. It reacts in 3H2O with a substrate amino acid and an apo-aminotransferase whose stereospecificity for C-4' hydrogen transfer is to be determined. The resultant pyridoxamine which is tritiated at C-4' is incubated with an apo form of aspartate aminotransferase or D-amino acid aminotransferase and a substrate, alpha-keto acid. The stereospecificity for the C-4' hydrogen transfer examined is determined by measurement of radioactivity retained in the pyridoxal formed. We showed by means of this method that C-4' hydrogen transfer of coenzyme occurs on the si face of the external Schiff base in the transamination reactions of two aspartate aminotransferases of Bacillus sp. YM-2 and Escherichia coli, and aromatic amino acid aminotransferase of E. coli.

Alanine Transaminase↗

PubMed1976

Histochemical evidence of aminotransferases.

The activity of the aspartate-, alanine-, tyrosine-, phenylalanine- and tryptophane aminotransferases in the rat organes in development have been investigated by quantitative histochemical methods. The isoenzymes have also been examined. The variable increase of the aminotransferase activity has been observed in the liver, brain, heart, skeletal muscle and kidney. In spite of the differences of the aspartate aminotransferase activity in the organs, the increase up to the 7th postnatal day, the reduction after that and the repeated increase after the 14th day reaching the level of the adult animals is evident as a common trend. A considerable increase of the alanine aminotransferase activity has been observed in the late postnatal period. While the difference in the activity of the aromatic aminotransferases in the embryonic organs is small, the changes of the 3 enzymes are different in the postnatal development. The number and the intensity of the isoenzymes of the aspartate- and alanine aminotransferases increase in the development. The isoenzyme spectrum of aromatic aminotransferases in the embryo proves an equal in number and intensity of fractions. In the development this similarity is preserved only with regard to cathode isoenzymes, while with anode once some differences appear.

Alanine Transaminase↗

PubMed2000

Hepatocellular proliferation in patients with chronic hepatitis C and persistently normal or abnormal aminotransferase levels.

BACKGROUND/AIMS: Some patients chronically infected with the hepatitis C virus (HCV) have persistently normal alanine aminotransferase (ALT) levels while progressive liver damage is observed histologically. In the present study, we compared the rate of proliferation, apoptosis, and necrosis in liver biopsy specimens of patients with persistently normal or elevated ALT levels. METHODS: Fourteen patients with persistently normal and 14 age- and sex-matched patients with elevated ALT levels were enrolled. Proliferation was detected using anti-Ki 67 in 10-microm liver biopsy specimens of the patients. Apoptosis was measured by TUNEL-assay and by monoclonal anti-M30 directed against caspase-cleaved cytokeratin 18 filaments. RESULTS: The mean number of anti-Ki 67 positive hepatocytes was lower in patients with persistently normal aminotransferases (3.1 +/- 2.8/10(3) vs 10.8 +/- 8.8/10(3) hepatocytes, p<0.0011) and was correlated with serum ALT (r=0.86, p<0.01) and aspartate aminotransferase levels (r=0.83, p<0.01). The rate of apoptosis detected by TUNEL assay was low and not different between patients with persistently normal and elevated aminotransferases. Staining with anti-M30 revealed a granular staining pattern and showed a trend towards higher cell death rates in patients with elevated aminotransferase levels (apoptotic hepatocytes with >75% staining: 3.97 +/- 6.24/10(3) hepatocytes vs 13.65 +/- 19.41/10(3) hepatocytes; p=0.08). CONCLUSIONS: Patients with chronic hepatitis C and normal aminotransferases have significantly lower hepatocyte proliferation rates and show a trend towards lower apoptosis rates compared with patients with elevated aminotransferases.

Adult↗

PubMed1997

Influence of hepatitis C virus (HCV) viraemia upon serum aminotransferase activity in chronic dialysis patients.

BACKGROUND: There are many reports concerning HCV in dialysis patients and most of them conclude that the clinical and biochemical features of hepatitis C are often silent in chronic dialysis patients. Elevated levels of serum alanine aminotransferase activity are a sensitive measure of hepatocellular injury, but so far the relationship between anti-HCV and ALT among chronic dialysis patients has been considered imperfect. To our knowledge, however, such an issue has not been adequately addressed. METHODS: Demographic, biochemical, and virological data from 506 patients undergoing chronic dialysis treatment in four dialysis units in Lombardy, northern Italy were collected in order to assess the influence of virological and host factors on serum aminotransferase values. RESULTS: Analysis of covariance showed that positivity for anti-HCV antibody was significantly associated with raised serum AST (P = 0.0001) and ALT (P = 0.0001) levels in the dialysis patients of the whole study group. Logistic regression analysis performed in the subset of patients tested for HCV viraemia and genotype showed that detectable HCV RNA in serum is a strong predictor of raised AST (P = 0.0001) and ALT (P = 0.000001) values. Gender showed an independent weak influence on AST levels (P = 0.055), serum levels of ferritin were significantly (P = 0.042) associated with AST values, the coexistence of HBsAg infection and positivity for anti-HCV antibody was independently associated with raised ALT levels (P = 0.016). The other factors (including positivity for anti-HCV) showed no independent effect on serum aminotransferase levels when they were matched with HCV viraemia in our multivariate analysis. HCV RNA positive patients showed serum AST (P < 0.008) and ALT levels (P < 0.0001) higher than HCV RNA negative patients. There was no relationship between HCV genotypes and liver enzymes. CONCLUSIONS: Our data show that detectable HCV RNA in serum is a strong independent predictor of raised aminotransferase values in chronic dialysis patients; the relationship between serum aminotransferase values and anti-HCV antibody was exclusively related to the association between raised aminotransferase values and HCV viraemia; HCV RNA positive patients show higher hepatic enzyme levels than dialysis patients with no detectable HCV RNA; no association between HCV genotype and serum aminotransferase activity was apparent.

Adult↗

PubMed2004

Correlation of serum aminotransferases with HCV RNA levels and histological findings in patients with chronic hepatitis C: the role of serum aspartate transaminase in the evaluation of disease progression.

OBJECTIVES: To investigate whether HCV RNA levels can be considered to be predictors of hepatocellular injury in patients with chronic hepatitis C, and whether aminotransferase levels are markers of liver damage. METHODS: We performed a retrospective study on 112 patients with chronic hepatitis C. For each patient, we considered the baseline alanine aminotransferase (ALT) and serum aspartate transaminase (AST) levels, baseline HCV RNA, HCV genotype, histological evaluation and the mean aminotransferase levels measured in the 6 months following liver biopsy. RESULTS: We found a statistically significant correlation between HCV RNA and aminotransferase levels measured during the follow-up (AST: r = 0.24, P = 0.01; ALT: r = 0.27, P = 0.004). We also observed a statistically significant correlation between HCV RNA levels and histological activity index (HAI) (r = 0.25, P = 0.008), as well as between the HAI and both baseline AST (r = 0.34, P = 0.0002) and ALT levels (r = 0.23, P = 0.01). These findings were confirmed by the mean aminotransferase values during follow-up. In the regression analysis, the fibrosis score was significantly and independently associated with baseline AST and ALT values. CONCLUSIONS: Our results demonstrate a statistically significant correlation of aminotransferase values with the histological parameters, and an even stronger correlation with the AST values. Our study therefore suggests that aminotransferase values, especially AST, may correlate with liver damage.

Adult↗

PubMed1995

Substitution of apolar residues in the active site of aspartate aminotransferase by histidine. Effects on reaction and substrate specificity.

In an attempt to change the reaction and substrate specificity of aspartate aminotransferase, several apolar active-site residues were substituted in turn with a histidine residue. Aspartate aminotransferase W140H (of Escherichia coli) racemizes alanine seven times faster (Kcat' = 2.2 x 10(-4) s-1) than the wild-type enzyme, while the aminotransferase activity toward L-alanine was sixfold decreased. X-ray crystallographic analysis showed that the structural changes brought about by the mutation are limited to the immediate environment of H140. In contrast to the tryptophan side chain in the wild-type structure, the imidazole ring of H140 does not form a stacking interaction with the coenzyme pyridine ring. The angle between the two ring planes is about 50 degrees. Pyridoxamine 5'-phosphate dissociates 50 times more rapidly from the W140H mutant than from the wild-type enzyme. A model of the structure of the quinonoid enzyme substrate intermediate indicates that H140 might assist in the reprotonation of C alpha of the amino acid substrate from the re side of the deprotonated coenzyme-substrate adduct in competition with si-side reprotonation by K258. In aspartate aminotransferase I17H (of chicken mitochondria), the substituted residue also lies on the re side of the coenzyme. This mutant enzyme slowly decarboxylates L-aspartate to L-alanine (Kcat' = 8 x 10(-5) s-1). No beta-decarboxylase activity is detectable in the wild-type enzyme. In aspartate aminotransferase V37H (of chicken mitochondria), the mutated residue lies besides the coenzyme in the plane of the pyridine ring; no change in reaction specificity was observed. All three mutations, i.e. W140-->H, I17-->H and V37--H, decreased the aminotransferase activity toward aromatic amino acids by 10-100-fold, while decreasing the activity toward dicarboxylic substrates only moderately to 20%, 20% and 60% of the activity of the wild-type enzymes, respectively. In all three mutant enzymes, the decrease in aspartate aminotransferase activity at pH values lower than 6.5 was more pronounced than in the wild-type enzyme, apparently due to the protonation of the newly introduced histidine residues. The study shows that substitutions of single active-site residues may result in altered reaction and substrate specificities of pyridoxal-5'-phosphate-dependent enzymes.

Animals↗

PubMed2003

Methionine regeneration and aminotransferases in Bacillus subtilis, Bacillus cereus, and Bacillus anthracis.

The conversion of ketomethiobutyrate to methionine has been previously examined in a number of organisms, wherein the aminotransferases responsible for the reaction have been found to be members of the Ia subfamily (L. C. Berger, J. Wilson, P. Wood, and B. J. Berger, J. Bacteriol. 183:4421-4434, 2001). The genome of Bacillus subtilis has been found to contain no subfamily Ia aminotransferase sequences. Instead, the analogous enzymes in B. subtilis were found to be members of the If subfamily. These putative aspartate aminotransferases, the yugH, ywfG, ykrV, aspB, and patA gene products, have been cloned, expressed, and characterized for methionine regeneration activity. Only YkrV was able to convert ketomethiobutyrate to methionine, and it catalyzed the reaction only when glutamine was used as amino donor. In contrast, subcellular homogenates of B. subtilis and Bacillus cereus utilized leucine, isoleucine, valine, alanine, phenylalanine, and tyrosine as effective amino donors. The two putative branched-chain aminotransferase genes in B. subtilis, ybgE and ywaA, were also cloned, expressed, and characterized. Both gene products effectively transaminated branched-chain amino acids and ketoglutarate, but only YbgE converted ketomethiobutyrate to methionine. The amino donor preference for methionine regeneration by YbgE was found to be leucine, isoleucine, valine, phenylalanine, and tyrosine. The B. subtilis ybgE gene is a member of the family III of aminotransferases and falls in a subfamily designated here IIIa. Examination of B. cereus and Bacillus anthracis genome data found that there were no subfamily IIIa homologues in these organisms. In both B. cereus and B. anthracis, two putative branched-chain aminotransferases and two putative D-amino acid aminotransferases were discovered as members of subfamily IIIb. These four sequences were cloned from B. cereus, expressed, and characterized. Only the gene product from the sequence designated Bc-BCAT2 was found to convert ketomethiobutyrate to methionine, with an amino donor preference of leucine, isoleucine, valine, phenylalanine, and tyrosine. The B. anthracis homologue of Bc-BCAT2 was also cloned, expressed, and characterized and was found to be identical in activity. The aminooxy compound canaline was found to be an uncompetitive inhibitor of B. subtilis YbgE and also inhibited growth of B. subtilis and B. cereus in culture.

Amino Acid Sequence↗

PubMed1979

Distribution of two aminotransferases and D-amino acid oxidase within the nephron of young and adult rats.

In the adult rat kidney, alanine aminotransferase (EC 2.6.1.2), aspartate aminotransferase (EC 2.6.1.1) and D-amino acid oxidase (EC 1.4.3.3) were measured in glomeruli, 4 parts of the proximal tubule, 2 parts of the distal tubule and in patches from the thin limb area and the papilla. These enzymes were measured in more limited parts of the nephron during postnatal development. Adult aspartate aminotransferase activities (percentage of the highest) ranged from 100 in the distal straight segment to 25 in the late part of the proximal straight segment to 10 in the thin limb and papillary area. Alanine aminotransferase (lower by a factor of 100 in absolute terms) was distributed as the mirror image of aspartate aminotransferase within proximal and distal tubules. D-Amino acid oxidase was 850-fold higher in proximal straight segments than in medullary structures. During development alanine aminotransferase increased 6-fold and D-amino acid oxidase, 4.5-fold in proximal straight tubules but aspartate aminotransferase increased in distal straight tubles 8-fold.

Aging↗

PubMedDate not supplied

[Activity of aminotransferases in the blue green alga Anacystis nidulans].

The blue-green alga Anacystis nidulans (strain L 1402-1) was grown at +37 degrees C in air (0.03 vol% CO2 and in air enriched with 3.0 vol% CO2. The effects of several inhibitors on the activity of aminotransferases, 14CO2 fixation and radioactive photosynthetic products of Anacystis were studied. No serine-pyruvate aminotransferase activity could be found in 10-2 M isonicotinyl hydrazide (INH); under the influence of this inhibitor aspartate and alanine aminotransferase were decreased about 49% respectively 17.6%. Serine-pyruvate and alanine aminotransferase activity decreased to more than 50% in 10-3 M glyoxalbisulfite. The obtained inhibitory effect of 10-4 M HPMS on serine-pyruvate aminotransferase (35%) was stronger than one the other aminotransferases. DCMU (5 x 10-6 M) inhibition on alanine aminotransferase activity was 83.7%. Under the influence of 10-3 M glyoxalbisulfite no 14C-labelled amino acids could be detected after 5 min photosynthesis; 14C-labelling of phosphoenolpyruvate, malate, phosphoglycolate and glycolic acid increased. Isonicotinyl hydrazide (10-2 M) caused in comparison to the control experiment a lower radioactivity in aspartate glutamate and phosphoenolpyruvate. The results are discussed with reference fo the operation of the glycolate pathway and a carboxylation reaction of phosphoenol-pyruvate in the blue-green alga Anacystis nidulans.

Alanine Transaminase↗

PubMed1981

Alanine aminotransferase and some other enzymes in different populations of free brain cortex mitochondria.

The activity of certain key enzymes involved in glutamic acid metabolism was studied in purified brain mitochondria and in mitochondrial subfractions separated in a discontinuous 1.2--1.6 mol/l sucrose gradient. Alanine aminotransferase and glutamate dehydrogenase were found to be matrix enzymes and aspartate aminotransferase to be associated with the inner mitochondrial membranes. After the purified mitochondria had been separated into 5 subfractions, aspartate aminotransferase and NAD+-dependent isocitrate dehydrogenase were found to be bound to the lighter mitochondrial subfractions settling at the 1.4--1.5 mol/l sucrose boundary while alanine aminotransferase, 4-aminobutyrate transaminase and glutamate dehydrogenase were associated with the heavier subfractions settling below 2.4 mol/l sucrose. The highest specific activity of the given enzymes was found in the subfraction settling at the 1.4--1.5 mol/l sucrose boundary, the only exception being alanine aminotransferase activity, whose maximum was found in the subfractions settling in 1.5 and 1.6 mol/l sucrose. It was concluded that alanine aminotransferase, in conjunction with glutamate dehydrogenase, is linked to NH3 binding and to the oxidation of reduced adenine nucleotides; in addition, alanine aminotransferase is presumed to have the function of transporting glutamate from the mitochondria to the extramitochondrial space.

4-Aminobutyrate Transaminase↗