Observations on the substrate specificity of DOPA decarboxylase from ox adrenal medulla, human phaeochromocytoma and human argentaffinoma.

The substrate specificity of the dopa decarboxylases of ox adrenal medulla, human phaeochromocytoma and human argentaffinoma have been studied. The enzymes from all three tissues decarboxylated dopa, metatyrosine, orthotyrosine and 5-hydroxytryptophan. Dopa was decarboxylated most rapidly and 5-hydroxytryptophan least rapidly by the enzyme from all three tissues. Competition experiments indicate that all four substrates are decarboxylated by the one enzyme. Attempts to demonstrate decarboxylation of [C(14)]-tyrosine, [C(14)]-tryptophan or [C(14)]-histidine by these enzyme preparations were unsuccessful.