Effect of pyridoxal 5-phosphate on carbidopa and decarboxylation of levodopa

To study the interaction between enzymes and coenzymes and carbidopa and levodopa, a paired-ion high-pressure liquid chromatographic method was developed to separate carbidopa, dopamine, levodopa, and pyridoxal 5-phosphate. Carbidopa strongly reacted with pyridoxal 5-phosphate, contrary to a previous report. Tyrosine decarboxylase and tyrosine decarboxylase apoenzyme had some activity against levodopa, which could be increased by adding pyridoxal 5-phosphate to the mixture. This activity was inhibited by hydroxylamine hydrochloride.