Glutamic aspartic transaminase

Glycolytic flux through the Embden— Myerhof pathway is obviously decreased in hypoglycaemia, contributing to a decreased cerebral metabolic rate for glucose (CMRgl) (Abdul-Rahman and Siesjo, 1980). Transamination reactions occur, and the aspartate—glutamate transaminase reaction is shifted to the left (Fig. 3.1). 

Fig. 3.1 Altered metabolism of excitatory amino acids during hypoglycemic coma. Oxaloacetate and a-ketoglutarate are the corresponding a-keto-acids to aspartate and glutamate, respectively. During hypoglycemia the aspartate—glutamate transaminase reaction is driven to the left...

The oxidation of L-aspartate (but not of the D-isomer) was accomplished by Nakada and Weinhouse" with washed homogenates of rat liver, upon the addition of either AMP or ATP. The interpretation of the authors is that the oxidation of L-aspartate is not due to a specific oxidase, but that it is caused by the transamination of the amino acid to oxal-acetate, which is subsequently oxidized through the operation of the citric acid cycle. The occurrence of aspartic-glutamic transaminase was demonstrated by assay and by the accumulation of glutamic acid. 

This enzyme [EC 2.6.1.21], also known as D-aspartate aminotransferase, D-amino acid aminotransferase, and D-amino acid transaminase, catalyzes the reversible pyridoxal-phosphate-dependent reaction of D-alanine with a-ketoglutarate to yield pyruvate and D-glutamate. The enzyme will also utilize as substrates the D-stereoisomers of leucine, aspartate, glutamate, aminobutyrate, norva-hne, and asparagine. See o-Amino Acid Aminotransferase... 

Fig. 42.13. Amino acid metabolism in the gut. The pathways of glutamine metabolism in the gut are the same whether it is supplied by the diet (postprandial state) or from the blood (postabsorptive state). Cells of the gut also metabolize aspartate, glutamate, and BCAA. Glucose is converted principally to the carbon skeleton of alanine. a-KG = a-ketoglutarate GDH = glutamate dehydrogenase TA = transaminase.

Little is known about the NADH aitd NAD content of the cytosol. In order to estimate the NADH/NAD ratio, the cytosolic contents of malate, aspartate, glutamate and 2-oxoglutarate were determined by nonaqueous fractionation of spinach leaves (Table l). From these values the NADH/NAD ratio was calculated on the reasonable assumption that the reactions catalyzed by the cytosolic malate dehydrogenase and glutamate oxaloacetate transaminase are near to equilibrium. Introducing the equilibrium constants of these enzymes 2.8. 10 at pH 7.0 (4), Kqqt... 

All the naturally occurring amino acids can in vivo participate in transamination reactions catalysed by transaminases. The reactions are universal in the biosphere in which they play an important role. They form important metabolic links between aspartate, glutamate and alanine on the one hand, and their corresponding a-keto acids in the tricarboxylic acid cycle on the... 

Pyridoxamine phosphate serves as a coenzyme of transaminases, e.g., lysyl oxidase (collagen biosynthesis), serine hydroxymethyl transferase (Cl-metabolism), S-aminolevulinate synthase (porphyrin biosynthesis), glycogen phosphoiylase (mobilization of glycogen), aspartate aminotransferase (transamination), alanine aminotransferase (transamination), kynureninase (biosynthesis of niacin), glutamate decarboxylase (biosynthesis of GABA), tyrosine decarboxylase (biosynthesis of tyramine), serine dehydratase ((3-elimination), cystathionine 3-synthase (metabolism of methionine), and cystathionine y-lyase (y-elimination). 

Aminotransferase (transaminase) reactions form pymvate from alanine, oxaloacetate from aspartate, and a-ketoglutarate from glutamate. Because these reactions are reversible, the cycle also serves as a source of carbon skeletons for the synthesis of these amino acids. Other amino acids contribute to gluconeogenesis because their carbon skeletons give rise to citric acid cycle... 

SCOT (AST) Serum glutamic oxaloacetic transaminase (aspartate TCN Tetracycline... 

Glutamate oxalacetic transaminase (SGOT), now frequently referred to as aspartate aminotransferase (AST)... 

As examples, two enzymes that will be discussed again later in this chapter are alanine transaminase (alanine aminotransferase) and aspartate transaminase (aspartate aminotransferase). In both cases, the amino group is transferred to 2-oxoglutarate (also known as a-ketoglutarate), which is oxoacid, above, forming glutamate as amino acid2. For example, the alanine transaminase (ALT) reaction is ... 

In effect, glutamate has been synthesized from 2-oxoglutarate, at the expense of alanine. Similarly, the interconversion of aspartate and glutamate catalysed by the enzyme aspartate transaminase (AST) ... 

Although aspartate and alanine have been identified in the description above as the amino group donor , the Keq for transaminase reactions is close to 1.0 so both reactions are, as indicated by the double-headed arrows, are easily reversible. Glutamate could just as easily act as the amino group donor if either reaction proceeds from right to left, resulting in the formation of alanine or aspartate respectively. 

EC2.6.1.1 L-aspartate aminotransferase (glutamate oxaloacetate transaminase) (aminotransferase (transaminase))... 

Aminotransferases have received many names as fashions in nomenclature have changed. Two obsolete names are still used in chnical practice glutamate-oxaloacetate transaminase (abbreviated to GOT) is now aspartate aminotransferase, and glutamate-pyruvate transaminase (GPT) is now alanine aminotransferase. The new abbreviations are AST and ALT, respectively. 

This enzyme [EC 2.6.1.1] (also known as transaminase A, glutamicioxaloacetic transaminase, and glutamic aspartic transaminase) catalyzes the reversible reaction of aspartate with a-ketoglutarate to produce oxaloace-tate and glutamate. Pyridoxal phosphate is a required cofactor. The enzyme has a relatively broad specificity, and tyrosine, phenylalanine, and tryptophan can all serve as substrates. 

This pyridoxal-phosphate-dependent enzyme [EC 2.6.1.5], also known as tyrosine transaminase, catalyzes the reaction of L-tyrosine with a-ketoglutarate (or, 2-oxoglutarate) to produce 4-hydroxyphenylpyruvate and L-glutamate. L-Phenylalanine can act as the substrate instead of tyrosine. In some systems, the mitochondrial enzyme may be identical with aspartate aminotransferase. 

AST aspartate transaminase previously known as SGOT (serum glutamate oxalate transaminase). 

Inhalation exposure of male Sprague-Dawley rats to 2-nitropropane at air concentrations of 100 ppm [365 mg/m ] for 7 h per day on four consecutive days did not result in increased hepatic microsomal malonaldehyde content as a measure of lipid peroxidation, or increased levels of serum aspartate transferase or of glutamic oxaloacetic transaminase. Total hepatic glutathione was enhanced by 2-nitropropane treatment (Haas-Jobelius et al., 1992). 

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