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Metabolism and Enzymology

Cytochrome P-450-Dependent Hydroxylation of Lauric Acid at the Subterminal Position and Oxidation of Unsaturated Analogs in Wheat Microsomes ¹

Département d'Enzymologie Cellulaire et Moléculaire, Institut de Biologie Moléculaire des Plantes, Centre National de la Recherche Scientifique UPR 406, 28, rue Goethe, F-67083 Strasbourg Cedex, France, Laboratoire de Chimie Bio-organique, Faculté de Pharmacie, Centre National de la Recherche Scientifique, URA 1386, 74 route du Rhin, F-67048 Strasbourg Cedex, France

Microsomes from etiolated wheat (Triticum aestivum L. cv Etoile de Choisy) shoots catalyzed the reduced nicotinamide adenine dinucleotide phosphate-dependent hydroxylation of lauric acid predominantly at the subterminal or (-1) position (65%). Minor amounts of 10-hydroxy- (31%) and 9-hydroxylaurate (4%) were also formed. The reaction was catalyzed by cytochrome P-450, since enzyme activity was strongly inhibited by tetcyclacis, carbon monoxide, and antibodies against NADPH-cytochrome c (P-450)-reductase. The apparent K_m for lauric acid was estimated to be 8.5 ± 2.0 µM. Seed treatment with the safener naphthalic acid anhydride or treatment of seedlings with phenobarbital increased cytochrome P-450 content and lauric acid hydroxylase (LAH) activity of the microsomes. A combination of both treatments further stimulated LAH activity. A series of radiolabeled unsaturated lauric acid analogs (8-, 9-, 10-, and 11-dodecenoic acids) was used to explore the regioselectivity and catalytic capabilities of induced wheat microsomes. It has been found that wheat microsomes catalyzed the reduced nicotinamide adenine dinucleotide phosphate-dependent epoxidation of sp2 carbons concurrently with hydroxylation at saturated positions. The regioselectivity of oxidation of the unsaturated substrates and that of lauric acid were similar. Preincubation of wheat microsomes with reduced nicotinamide adenine dinucleotide phosphate and 11-dodecenoic acid resulted in a partial loss of LAH activity.

¹ This work was supported by the Centre National de la Recherche Scientifique and by a Ministère de la Recherche et de la Technologie grant to A.Z.

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