ENZYMIC ASSAY OF PYRIDOXAL PHOSPHATE USING TYROSINE APODECARBOXYLASE AND TYROSINE-1-14C

A new approach for determination of pyridoxal phosphate in biological material is reported. The principle of the method is based on the decarboxylation reaction of l-tyrosine catalyzed by l-tyrosine decarboxylase (l-tyrosine carboxy-lyase, EC 4.1.1.25) in the presence of pyridoxal phosphate. l-Tyrosine-1-14C was used as the substrate and the rate of decarboxylation reaction was followed by a decrease of the radioactivity of the reaction mixture. Preparation of cell-free and pyridoxal phosphate free tyrosine apodecarboxylase was described. By this method, pyridoxal phosphate can be assayed for quantities of less than 5 ng. Concentrations of pyridoxal phosphate in whole blood, brains, and livers from both pyridoxine deficient and normal rats were also reported. © 1969.