2-Aminobenzoylpyruvic acid

It was only many years after the discovery of tryptophan that a plausible degradative pathway could first be outlined, but during this early period a few tryptophan metabolites were identified. The long-known (559) kynurenic acid (structure, diagram 20 cf. 408) was shown in 1904 to be derived from tryptophan (220), but the considerable amount of work on kynurenic acid formation (reviewed by Neubauer, 637) gave few useful results. Neubauer (637), however, made the plausible (and correct) suggestion that it was derived from o-aminobenzoylpyruvic acid (structure, diagram 20). 

Knox et al. (176) found that formation of anthranilic acid from kynurenine was always accompani by formation of kynurenic acid, and they considered that the keto acid (o-aminobenzoylpyruvic acid, diagram 20) might be a common intermediate in formation of both substances. This was soon disproved, and it is now clear that two independent reactions are involved, as illustrated in diagram 20. 

The enzyme is active on both L-kynurenine and L-3-hydroxykynurenine. The D-isomers are inert. It requires pyridoxal phosphate as a coenzyme. The most effective amino-group acceptor is a-ketoglutarate, but other a-keto acids can also function. o-Aminobenzoylpyruvic acid, the expected product of the action of kynurenine transaminase on kynurenine, has not... 

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