Glutamate-aspartate transaminase

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. 

Sizer, I. W., and Jenkins, W. T. (1962). Glutamic Aspartic Transaminase from Pig Ventricles Preparation and Assay of Enzymes. Methods Enzymol 5 677. Stryer, L. (1995). Amino Acid Degradation and the Urea Cycle. In Biochemistry, 4th ed. New York Freeman. 

Boettcher, B., and Martinez-Carrion, M. (1975). Biochem. Biophys. Res. Comm. 64, 28. Glutamate Aspartate Transaminase Modified at Cysteine 390 with Enriched Carbon-13 Cyanide. 

Obviously, the elucidation of the enzymic mechanism required the preliminary purification of at least one of the transaminases. An 85-90% pure glutamic aspartic transaminase was obtained and found to contain 2 moles of pyridoxal phosphate per mole of enzyme. But pyridoxal is not the active coenzyme. Gunsalus, Bellamy, and Umbreit discovered that the addition of pyridoxal to a culture medium of a strain of Streptococcus faecalis grown on a pyri-doxal-deficient medium has little effect on the ability of the bacteria to decarboxylate tyrosine. When the culture was supplemented with pyridoxal and adenosine triphosphate, or with phosphorylated derivatives of pyridoxal, the tyrosine decarboxylation activity was greatly enhanced. It was later established that... 

An example is the glutamate-aspartate transaminase which catalyses the reaction... 

If this were indeed the mechanism of action of pyridoxal phosphate, then one would think that either pyridoxal or pyridoxamine phosphate would be active in catalyzing the enzymatic transamination. In one case recently with a highly purified glutamic aspartic transaminase only pyridoxal phosphate was capable of reconstituting the system. 

In animal tissues cysteinesulfinic acid can undergo transamination, decarboxylation, and oxidation. In certain strains of Proteus vulgaris an alternative oxidation and transamination operate simultaneously 18). It was shown by Cohen 19) and by Kearney and Singer 18) that both in animal and microbial systems the transamination of cysteine sulfinate catalyzed by glutamate-aspartate transaminase proceeds as follows ... 

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