Toxopyrimidine phosphate as an inhibitor of bacterial enzyme systems that require pyridoxal phosphate

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Abstract
Toxopyrimidine phosphate failed to inhibit unresolved bacterial arginine and glutamic decarboxylases, tryptophanase and glutamate-alanine transaminase. The leucine decarboxylase system of Proteus vulgaris, in which the coenzyme dissociates spontaneously during enzyme action, was inhibited by 20%. The degree of inhibition of the resolved tyrosine decarboxylase system of Streptococcus faecalis depended on the order of addition of pyridoxal phosphate and toxopyri-midine phosphate to the apoenzyme. Even when the inhibitor was added first, an inhibitor: coenzyme ratio of 1000:1 was needed to produce 50% inhibition. Toxopyrimidine phosphate seems to be of only limited usefulness in the study of bacterial vitamin Bg enzymes.