The relative sensitivity of pyridoxal phosphate-dependent enzymes to inhibition in vitro.

The effect of carbonyl and non-carbonyl reagents on five pyridoxal phosphate-dependent enzymes in vitro is described. Specific histidine decarboxylase of rat stomach and non-specific histidine decarboxylase (aromatic L-amino acid decarboxylase) of guinea-pig kidney are more susceptible to inhibition than are aspartate aminotransferase of pig heart, glutamic acid decarboxylase of mouse brain and kynurenine aminotransferase of rat kidney. This greater effect of inhibitors on the histidine decarboxylases is particularly marked in the case of carbonyl reagents, and it should limit the number of untoward side effects which might result from the inhibition of other pyridoxal phosphate-dependent enzymes when these compounds are used in vivo.