Abstract
Summary In cell-free extracts of pea leaves, the oxidation of hypoxanthine to xanthine and uric acid was catalyzed by a NAD + -dependent xanthine dehydrogenase. Considerable activity was also observed with NADP + as electron acceptor. However, little activity was detected with oxygen (air) alone. Comparative tests in the presence of a variety of artificial electron acceptors showed high activity for phenazine methosulphate, but only low activity for methylene blue, nitro blue tetrazolium, 2,6-dichlorophenol indophenol, and K 3 Fe(CN) 6 . It was not possible to convert the xanthine dehydrogenase to an oxidase form. The xanthine dehydrogenase activity was inhibited by KCN and allopurinol, known inhibitors of xanthine oxidase. Inhibition by salicylhydroxamic acid indicated the presence of non-heme iron. Xanthine dehydrogenase of pea leaves was not associated with any major subcellular particulate fraction (mitochondria, chloroplasts, peroxisomes, microsomes) but appeared to be a soluble enzyme of the cytoplasm.
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