Flavin Nucleotide-Dependent 3-Hydroxylation of 4-Hydroxyphenylpropanoid Carboxylic Acids by Particulate Preparations from Potato Tubers

Particulate preparations from potato tubers, extracted in 4 mᴍ 2-m ercaptoethanol, catalyze the 3-hydroxylation of 4-hydroxyphenylpropanoid carboxylic acids, including p-coumaric acid and tyrosine, in the presence of NADH (or NADPH) and FAD (or FMN); ascorbate could not substitute for these electron donors. Among a range of 4-hydroxylated C6-C2 and C6-C1 compounds tested, only 4-hydroxyphenylacetic acid and p-cresol were hydroxylated. The hydroxylase was sensitive to KCN and diethyldithiocarbam ate and showed some features of phenolase hydroxylation, but no DOPA oxidase nor chlorogenic acid oxidase activity was exhibited under these conditions. It is suggested that the phenolase complex, which is confined to potato tuber particles, in whole or part catalyzes the hydroxylation.