The oxidation of pyridoxal and related compounds by pea-seedling extracts or systems containing peroxidase

Abstract

Pyridoxal, pyridoxal phosphate, pyridoxine and pyridoxamine increase the oxygen uptake of pea-seedling extracts in the presence of 1,4-diaminobutane. These increases are greatest with root extracts and are accompanied by a disappearance of pyridoxal or related compounds. Two thermolabile factors in pea-seedling extracts, probably a diamine oxidase and a peroxidase, are involved in this reaction. The diamine oxidase and 1,4-diaminobutane can be replaced by hydrogen peroxide or another system that produces hydrogen peroxide. Pyridoxal and related compounds containing the 3-hydroxypyridine structure are substrates for peroxidase; when pyridoxal or pyridoxine are incubated with pea-seedling root extracts and 1,4-diaminobutane or with peroxidase and a hydrogen peroxide producing system, the 3-hydroxypyridine structure is destroyed. The increase in oxygen uptake when pyridoxal is incubated with legume-seedling extracts catalysing the oxidation of diamines is therefore not, as has been suggested, evidence for a pyridoxal moiety in the prosthetic group of plant diamine oxidase but is due at least in part to a coupled oxidation of pyridoxal by peroxidase.