The oxidation of reduced pyridine nucleotides by peroxidase.

A soluble enzyme system which catalyzes the aerobic oxidation of reduced pyridine nucleotides in wheat germ has previously been described (1). Peroxidase was shown to be a component of this system. Later, Humphreys (2) demonstrated that Mn+ and an unidentified cofactor were required for aerobic oxidation of TPNH’ in crude preparations of malic enzyme from wheat germ. Although no attempt was made to demonstrate a peroxidase requirement in this work, the protein preparations used gave strongly positive tests for peroxidase. Recently Stern and Johnston (3) have investigated a particulate enzyme system in wheat embryos which has properties in common with those described by the earlier workers. The present study shows that reduced pyridine nucleotides are oxidized aerobically in the presence of horse-radish peroxidase, Mn+2, and certain phenols. The properties of this reaction are compared with those of other oxidations catalyzed by peroxidase, and a mechanism accounting for the oxidation of DPNH and TPNH is proposed.