Oxaloacetic transminase

There are numerous transminases, each specific to a given substrate pair. Some may be primarily mitochondrial others, cytosolic. For example, glutamate-oxaloacetate transminase (GOT), also called aspartate aminotransferase (AST), is primarily a mitochondrial enzyme. AST is extensively used in the diagnosis of heart and liver disorders (see Chapter 5). The AST reaction is represented by Equation (20.7). 

GOT glutamic oxaloacetic transminase MIT metabolic inhibition test. 

The enzymes glutamate-oxaloacetate transminase (GOI) is assayed by a coupled stem, having the following reactkais. 

A possible explanation for the superiority of the amino donor, L-aspartic add, has come from studies carried out on mutants of E. coli, in which only one of the three transaminases that are found in E. coli are present. It is believed that a branched chain transaminase, an aromatic amino add transaminase and an aspartate phenylalanine aspartase can be present in E. coli. The reaction of each of these mutants with different amino donors gave results which indicated that branched chain transminase and aromatic amino add transminase containing mutants were not able to proceed to high levels of conversion of phenylpyruvic add to L-phenylalanine. However, aspartate phenylalanine transaminase containing mutants were able to yield 98% conversion on 100 mmol l 1 phenylpyruvic acid. The explanation for this is probably that both branched chain transaminase and aromatic amino acid transminase are feedback inhibited by L-phenylalanine, whereas aspartate phenylalanine transaminase is not inhibited by L-phenylalanine. In addition, since oxaloacetate, which is produced when aspartic add is used as the amino donor, is readily converted to pyruvic add, no feedback inhibition involving oxaloacetate occurs. The reason for low conversion yield of some E. coli strains might be that these E. cdi strains are defident in the aspartate phenylalanine transaminase. 

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