THE ROLE OF PLANT PHENOLIC COMPOUNDS IN THE OXIDATION OF REDUCED DIPHOSPHOPYRIDINE NUCLEOTIDE BY PEROXIDASE

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Abstract
Horse-radish peroxidase and dialyzed extracts from pea epicotyls and from spruce shoots oxidized reduced diphosphopyridine nucleotide in the presence of p-coumaric acid. Maximum activity was obtained when hydrogen peroxide, Mn+2, p-coumaric acid, and enzyme were present. p-Hydroxyphenylpropionic acid, p-hydroxyphenylpyruvic acid, tyrosol, or resorcinol could replace p-coumaric acid as the phenolic activator but they were less efficient. Ferulic and sinapic acids were competitive inhibitors while chlorogenic acid, caffeic acid, and hydroquinone were non-competitive inhibitors of the reaction. The oxidation of the reduced coenzyme was inhibited by citrate and pyrophosphate, enhanced by versene, and delayed by ascorbic acid, cysteine, and reduced glutathione. The results indicate that the peroxidase system may be identical with the enzyme system which oxidizes indoleacetic acid.