Cytochrome P-450-Dependent omega-Hydroxylation of Lauric Acid by Microsomes from Pea Seedlings

Abstract

Microsomes from apical buds of pea (Pisum sativum L. var. Téléphone à rames) seedlings hydroxylate lauric acid at the omega-position. This oxidation is catalyzed by a cytochrome P-450 enzyme which differs from laurate hydroxylases previously described in microorganisms and mammals by its strict substrate specificity and the ability of low NADH concentrations to support unusually high oxidation rates. The apparent K(m) for lauric acid was 20 micromolar. NADPH- and NADH-dependent laurate hydroxylation followed non-Michaelian kinetics with apparent K(m) values ranging from 0.2 to 28 micromolar for NADPH, and 0.2 to 318 micromolar for NADH. When induced by the photomorphogenic photoreceptor phytochrome, the time course for the enhancement of laurate omega-hydroxylase was totally different from that of the cinnamic acid 4-hydroxylase, providing evidence for the existence of multiple cytochrome P-450 species in pea microsomes.