Abstract

A lauric acid monooxygenase which catalyzes the formation of hydroxylaurate from lauric acid has been characterized in ageing tissues of Jerusalem artichoke (Helianthus tuberosus L.) tuber. Three reaction products have been identified from the mass fragmentation pattern of their methyltrimethylsilyl derivatives: 10-hydroxylauric acid, 9-hydroxylauric acid and 8-hydroxylauric acid. Enzyme activity is located on the microsomal fraction which also carries cytochrome P-450 and NADPH cytochrome-c reductase. The apparent Km of the enzyme for lauric acid is 0.97 micronM. Laurate monooxygenation is dependent upon O2 and inhibited by CO. The latter effect is light reversible. NADPH is the preferred electron donor although appreciable NADH-sustained activity was observed. NADPH cytochrome c reductase is involved in electron transfer as evidenced by the inhibitory effects of NADP+ and oxidized cytochrome c on laurate monooxygenation. Thus, the enzyme catalyzing laurate oxidation in Jerusalem artichoke tuber tissues appears to be a typical (cytochrome P-450)-linked monooxygenase.