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PubMed1975

Purification and studies on some properties of the 4-aminobutyrate : 2-oxoglutarate transaminase from rat brain.

Using various chromatographic procedures, 4-aminobutyrate : 2-oxoglutarate transaminase from rat brain has been purified 2400 times with respect to the initial brain homogenate. The purified protein, which has a specific activity of 10 mumol times min -1, x mg-1 gave a single band by acrylamide gel electrophoresis and isoelectric focusing. It has a molecular weight of 105000 +/- 5000 and an isoelectric point of 6.8. In the presence of 0.1% sodium dodecylsulphate, a single protein band is seen on polyacrylamide gel, corresponding to a molecular weight of 57000 +/- 5000. N-terminal analysis reveals two chains with the same N-terminal amino acid, thus the enzyme may be considered as a dimer consisting of two identical subunits. The pH optimum for enzyme activity is 8.5. Studies of the enzymic reaction show that the general mechanism is of the ping-pong bi-bi model. The Km for 2-oxoglutarate at saturating 4-aminobutyrate extrapolated to saturating 2-oxoglutarate concentration is 4 mM. 2-Oxoglutarate competitively inhibits the enzyme with respect to 4-aminobutyrate, with a Ki of 1.8 times 10(-4) M. The same phenomenon is seen for the reverse reaction where the Ki is 6.6 times 10(-4) M for succinic semi-aldehyde.

4-Aminobutyrate Transaminase↗
PubMed1981

The biochemical genetics of human gamma-aminobutyric acid transaminase.

1. Two methods have been devised for the detection after electrophoresis of gamma-aminobutyric acid transaminase (GABAT) isozymes. 2. GABAT isozymes can be detected in liver, brain, kidney, pancreas, heart, testis. spinal cord and upper jejunum. The greatest activity occurs in liver. 3. Three different commonly occurring electrophoretic types of GABAT have been identified. It seems likely that they are determined by two alleles at an autosomal locus (GABAT). 4. The gene frequencies of GABAT1 and GABAT2 in a random sample of European livers were 0.56 and 0.44 respectively. 5. The three banded patterns seen in heterozygotes suggest that GABAT is a dimeric enzyme. 6. GABA, beta-alanine and 5-aminovaleric acid can act as substrates for GABAT. 7. GABAT activity can be demonstrated in all areas of human brain with the exception of the corpus callosum. Brain samples from patients with Huntington's chorea show no abnormal GABAT activity or unusual phenotypes.

4-Aminobutyrate Transaminase↗
PubMed1981

The inactivation of gamma-aminobutyric acid transaminase in dissociated neuronal cultures from spinal cord.

It had previously been shown that dissociated cell cultures from chick embryo spinal cord have a high affinity uptake system for the neurotransmitter gamma-aminobutyric acid (GABA) and make functional inhibitory synaptic contacts as determined by electrophysiology (Farb et al., 1979). It is shown here that these cultures can synthesize GABA from added glutamate in a glutamate decarboxylase-dependent reaction. Furthermore, these cultures have a functional GABA transaminase that degrades the neurotransmitter. This enzyme can be specifically and irreversibly blocked with gabaculine. A 15 min incubation with 10(-6) M-gabaculine completely inactivates the enzyme. The inactivation of the enzyme leads to an increase in GABA levels. Long-term incubation (16 days) of gabaculine in the medium does not appear to alter high affinity GABA transport, suggesting that the drug is not toxic to cells capable of accumulating GABA.

4-Aminobutyrate Transaminase↗
PubMed1983

GABA, glutamic acid decarboxylase, and GABA transaminase levels in the myenteric plexus in the intestine of humans and other mammals.

Regional distribution of endogenous gamma-aminobutyric acid (GABA), its synthesizing enzyme, glutamic acid decarboxylase (GAD), and metabolic enzyme, GABA transaminase (GABA-T), were determined in the intestinal tract of guinea pigs and cats and the findings compared with the number of ganglion cells in Auerbach's plexus. There were positive correlations among the GABA contents and the numbers of neural cells of the plexus. The precise localization of GABA and GAD in individual layers (mucosa, circular and longitudinal muscles, and Auerbach's plexus) in the human and cat colon was also determined. The endogenous GABA contents and GAD activity were the highest in Auerbach's plexus in tissues of both species. These results indicate that GABA is synthesized and localized in Auerbach's plexus and probably plays a significant role in the enteric nervous system.

4-Aminobutyrate Transaminase↗
PubMed1980

Investigation of the antifibrillatory activity of some anticonvulsant gamma-aminobutyric acid-transaminase inhibitors in the rabbit isolated heart: comparison with phenytoin and mexiletine.

1 The electrical stimulation and ventricular fibrillation thresholds were measured in the Langendorff-perfused rabbit heart by application of rectangular impulses of 3 ms duration and increasing current at frequencies of 4 and 20 Hz respectively. 2 Perfusion with either phenytoin or mexiletine produced significant dose-dependent increases in both thresholds. 3 Perfusion with four anticonvulsant inhibitors of gamma-aminobutyric acid (GABA)-transaminase, aminooxyacetic acid, gamma-acetylenic GABA, gamma-vinyl GABA and sodium valproate, up to a concentration of 20 microgram/ml, had no significant effect on either threshold. 4 The results suggest that these compounds, unlike phenytoin and mexiletine, are devoid of antifibrillatory activity.

4-Aminobutyrate Transaminase↗
PubMed1980

Seizure protection and increased nerve-terminal GABA: delayed effects of GABA transaminase inhibition.

Changes in gamma-aminobutyric acid (GABA) occurring in the presence and in the absence of GABA-containing nerve terminals were estimated in rats in which the dense GABA projection to the substantia nigra was surgically destroyed on one side of the brain. The net increase in GABA of the denervated nigra was compared with that of the intact nigra at various times after a single injection of gama-vinyl-GABA, which irreversibly inhibits GABA transaminase. Total GABA reached a maximum within 12 hours, but the GABA pool associated with nerve terminals did not increase until 36 hours and peaked at 60 hours. The onset and peak of anticonvulsant activity against maximal electroshock seizures directly paralleled the time course for the increase in GABA in nerve terminals, but was not positively correlated with that independent of the terminals. This result supports the concept that elevating GABA in nerve terminals facilitates GABA-mediated synaptic transmission and predicts anticonvulsant activity.

4-Aminobutyrate Transaminase↗
PubMed2004

omega-Amino acid:pyruvate transaminase from Alcaligenes denitrificans Y2k-2: a new catalyst for kinetic resolution of beta-amino acids and amines.

Alcaligenes denitrificans Y2k-2 was obtained by selective enrichment followed by screening from soil samples, which showed omega-amino acid:pyruvate transaminase activity, to kinetically resolve aliphatic beta-amino acid, and the corresponding structural gene (aptA) was cloned. The gene was functionally expressed in Escherichia coli BL21 by using an isopropyl-beta-D-thiogalactopyranoside (IPTG)-inducible pET expression system (9.6 U/mg), and the recombinant AptA was purified to show a specific activity of 77.2 U/mg for L-beta-amino-n-butyric acid (L-beta-ABA). The enzyme converts various beta-amino acids and amines to the corresponding beta-keto acids and ketones by using pyruvate as an amine acceptor. The apparent K(m) and V(max) for L-beta-ABA were 56 mM and 500 U/mg, respectively, in the presence of 10 mM pyruvate. In the presence of 10 mM L-beta-ABA, the apparent K(m) and V(max) for pyruvate were 11 mM and 370 U/mg, respectively. The enzyme exhibits high stereoselectivity (E > 80) in the kinetic resolution of 50 mM D,L-beta-ABA, producing optically pure D-beta-ABA (99% enantiomeric excess) with 53% conversion.

Achromobacter denitrificans↗
PubMed1975

Two forms of 4-aminobutyrate transaminase in guinea pig brain.

4-Aminobutyrate transaminase (GABA-T, 4-aminobutyrate alpha-oxoglutrate aminotransferase, EC 2.6.1.19) is an enzyme that inactivates the inhibitory neurotransmitter, GABA, but its pharmacological function is uncertain. Two forms of guiena pig brain GABA-T were isolated by DEAE-cellulose chromatography and designated as GABA-T-I and II, corresponding to an anionic and a cationic form. The enzymes were inhibited by high concentrations of a cationic form. The enzymes were inhibited by high concentrations of alpha-oxoglutrate (alpha-KG). Kinetic consists for GABA, when determined at pH 7.9 adn 1 mmol/l alpha-KG, were 0.74 mmol/l. GABA-T activity was inhibited by chloride and other anions. Kinetic analysis revealed chloride ion as a conpetitive inhibitor against GABA, but the Ki values differed among GABA-T-I and II (Ki equals 120 and 60 mmol/l, respectively). Similar degrees of difference were observed with acetate and lactate ion. These results suggest that GABA-T-II may regulate the GABA level in the inhibitory neurons and may play a similar functional role as that exhibited by monoamine oxidase in other synapses.

4-Aminobutyrate Transaminase↗
PubMed1981

Treatment of Huntington disease with gamma-acetylenic GABA an irreversible inhibitor of GABA-transaminase: increased CSF GABA and homocarnosine without clinical amelioration.

gamma-Acetylenic GABA (GAG, RMI 71.645), a potent irreversible inhibitor of gamma-aminobutyric acid transaminase, was given orally in various dosage schedules to 14 patients with Huntington disease. The biochemical effects of the drug on cerebrospinal fluid (CSF) concentrations of gamma-aminobutyric acid (GABA) and the GABA-containing dipeptide, homocarnosine, were measured in 10 of 14 patients. Treatment with GAG increased CSF concentrations of GABA and homocarnosine as compared to pretreatment values, suggesting that the drug increased brain GABA concentration. Despite this neurochemical effect, the clinical state was not improved. Except for single seizure episodes in five patients, GAG therapy was well tolerated. These results do not exclude the possibility that agents that augment CNS GABAergic function may prove useful in therapy of Huntington disease.

4-Aminobutyrate Transaminase↗
PubMedDate not supplied

The role of imipramine hydrochloride on plasma transaminase and glucose level on rats under altitude stress.

The effect of exposure of albino rats to simulated high altitude stress of 5000 metres for 3 and 6 hrs on plasma transaminases, non-protein nitrogen (NPN), total protein percentages and blood sugar levels have been studied both with and without the administration of an anti-stress drug Imipramine HCl at 2.0 mg/kg body weight. The drug appears to have a slight hepatotoxic effect.

Alanine Transaminase↗
PubMed1992

Tyrosine aminotransferase: a transaminase among others?

Tyrosine aminotransferase (L-tyrosine: 2 oxoglutarate aminotransferase; EC 2.6.1.5; TATase) is the first enzyme in the catabolic pathway of tyrosine. The gene of this transaminase is regulated by glucocorticoid hormones as well as via the cAMP pathway. This review gives a brief survey of the structural and physico-chemical properties of this well-known protein. A comparative study of the properties of TATase with other aminotransferases is also included to analyse this molecule for itself, and not only as a marker used in studies on enzymatic induction. Finally, the regulation of the gene expression is presented, in order to underline a few important features of this model.

Amino Acid Sequence↗
PubMed1976

[Inhibition of 4-aminobutyrate transaminase by ethanolamine-O-sulfate].

The analysis of the interaction of ethanolamine-O-sulphate with 4-aminobutyrate transaminase revealed that the inhibitory effect is exerted upon the substrate subsite of the active site of the enzyme in aldimine form. The inhibition in irreversible. The inactivation rate versus pH-curve was shown to have a sigmoid character with inclination point at neutral pH. The study of inhibition kinetics by the Kitz and Wilson method revealed a complex inhibitory pattern compatible with a minimal two-step mechanism. Rate constant of inactivation was found to be equal to 0.22 min-1 and the value of the inhibitory constant--to 1.1-10(-2) M.

4-Aminobutyrate Transaminase↗
PubMed1988

Pyridoxine effects on ornithine ketoacid transaminase activity in fibroblasts from carriers of two forms of gyrate atrophy of the choroid and retina.

Gyrate atrophy of the choroid and retina that is due to ornithine ketoacid transaminase (OKT) deficiency is an autosomal recessive disorder. Fibroblasts from heterozygotes for the pyridoxine-responsive variant as well as those for the pyridoxine-nonresponsive variant contain intermediate levels of OKT activity. These two variants can be distinguished by the in vitro responsiveness of OKT activity to pyridoxal phosphate (PLP) stimulation. The ratios of OKT activity at 0.04 mM PLP compared with activity at 0 mM PLP were, respectively, lowest for controls (1.18 +/- 0.18; N = 12), intermediate for pyridoxine-nonresponsive heterozygotes (1.43 +/- 0.26; N = 5), and highest for pyridoxine-responsive heterozygotes (2.20 +/- 0.14; N = 3).

Atrophy↗
PubMed1988

Branched chain amino acid transaminases in brain in methionine sulphoximine (MSI) toxicity.

The effect of intraperitoneal administration of L-methionine-DL-sulphoximine (MSI) was studied on branched-chain amino acid transaminases (BCAA-T) in different regions of rat brain and in liver. Administration of an acute dose of MSI (300 mg/kg body weight) resulted in a significant decrease in leucine aminotransferase activity in cerebral cortex, cerebellum, and brain-stem, while the activity of isoleucine aminotransferase was enhanced in hippocampus, corpus striatum, brain stem, and midbrain. Activities of both these enzymes changed marginally or remained unaltered in other regions of the brain. Valine aminotransferase showed a significant decrease in all the regions of the brain except in cerebellum. Following the administration of a sub-acute dose of MSI (150 mg/kg body wt.), the activities of the three BCAA aminotransferases were found to be enhanced in all regions of the brain. The results are discussed in relation to the utilization of BCAA for the production of glutamate and glutamine in hyperammonemia.

Animals↗
PubMed1978

Influence of a GABA transaminase inhibitor on central nervous system oxygen toxicity.

A decrease in brain GABA concentration has been implied as the cause of convulsions induced by hyperbaric oxygen (HOP). We therefore examined the influence of sodium valproate, an anticonvulsant and GABA transaminase inhibitor on HOP-induced convulsions in rats. The mean latency of occurrence of the first electrical discharge in the ECoG and the appearance of the first clinical seizure in awake chronically implanted rats was unchanged by administration of sodium valproate prior to HOP exposure. We conclude that either the sodium valproate inhibition of GABA removal is insufficient to compensate for HOP inhibition of its production, or else that GABA concentration changes are not causally related to HOP-induced seizures.

4-Aminobutyrate Transaminase↗
PubMed1979

[Quantitative histochemical study of the effect of benzodiazepine tranquilizers on cerebral GABA-transaminase activity].

The effect of diazepam and nitrazepam (0.5, 1, 2.5, and 5 mg/kg) on GABA-transaminase activity in the rat cerebellar cortex and hippocampus was investigated by quantitative histochemistry. Both the drugs suppressed the enzyme activity in the hippocampus; the maximal effect was produced by diazepam. It is suggested that the observed alterations are caused by the enzyme inhibition and also by a decrease of GABA turnover rate.

4-Aminobutyrate Transaminase↗
PubMedDate not supplied

[GABA-transaminase activity in the dog brain visual analyzer following light deprivation during ontogenesis].

The GABA-transaminase activity is the highest in the subcortical formations of the brain visual analyzer in 45- and 90-day dogs. Deprivation of visual impulses at early stages of postnatal ontogenesis lowers sharply this activity in all the studied areas of the brain visual analyzer. Under conditions of deprivation the content of glutaminic acid increases in all the formations of the dog brain visual analyzer to a considerably less extent, especially in the anterior corpora bigemina and lateral geniculate body at the age of 45- and 90-days. Similar regularities are found in the deprivation effect relative to formation of ascorbic acid the content of which lowers sharply in all the formations of the dog brain visual analyzer on the 90th day of light deprivation.

4-Aminobutyrate Transaminase↗