The enzymatic oxidation of pyridoxine and pyridoxamine phosphates.

Extracts of rabbit liver and brain are known (1, 2) to oxidize pyridoxine 5-phosphate to pyridoxal 5-phosphate much faster than they oxidize free pyridoxine to pyridoxal. Comparison of the two activities during limited purification indicated that different enzymes catalyzed the two reactions (1). Pogell (3) had shown previously that oxidation of pyridoxamine 5-phosphate was catalyzed by an enzyme present in rabbit liver. This enzyme was purified approximately 15-fold and was shown to be distinct from both monoamine oxidase and diamine oxidase. Further investigations of the purification and properties of pyridoxine 5-phosphate oxidase and of pyridoxamine 5-phosphate oxidase, reported herein, lead to the conclusion that the two enzymes are probably identical. In the course of these investigations, a simple photometric method has been developed for the determination of pyridoxal or pyridoxal S-phosphate in enzymatic reaction mixtures.