PLANT PHYSIOLOGY , Vol 102, Issue 4 1313-1318, Copyright © 1993 by American Society of Plant Biologists
|
METABOLISM AND ENZYMOLOGY |
[omega]-Hydroxylation of Oleic Acid in Vicia sativa Microsomes (Inhibition by Substrate Analogs and Inactivation by Terminal Acetylenes)
F. Pinot, H. Bosch, C. Alayrac, C. Mioskowski, A. Vendais, F. Durst and J. P. Salaun
Institut de Biologie Moleculaire des Plantes-Centre National de la Recherche Scientifique, Departement d'Enzymologie Cellulaire et Moleculaire, 28 rue Goethe, F-67083 Strasbourg Cedex, France (F.P., F.D., J.-P.S)
Oleic acid (18:1) is hydroxylated exclusively on the terminal methyl by a
microsomal cytochrome P-450-dependent system ([omega]-OAH) from
clofibrate-induced Vicia sativa L. (var minor) seedlings (F. Pinot, J.-P.
Salaun, H. Bosch, A. Lesot, C. Mioskowski, F. Durst [1992] Biochem Biophys
Res Commun 184: 183-193). This reaction was inactivated by two terminal
acetylenes: (Z)-9-octadecen-17-ynoic acid (17-ODCYA) and the corresponding
epoxide, (Z)-9,10-epoxyoctadecan-17-ynoic acid (17-EODCYA). Inactivation
was mechanism-based, with an apparent binding constant of 21 and 32 [mu]M
and half-lives of 16 and 19 min for 17-ODCYA and 17-EODCYA, respectively.
We have investigated the participation of one or more [omega]-hydroxylase
isoforms in the oxidation of fatty acids in this plant system. Lauric acid
(12:0) is [omega]-hydroxylated by the cytochrome P-450 [omega]-hydroxylase
[omega]-LAH (J.-P. Salaun, A. Simon, F. Durst [1986] Lipids 21: 776-779).
Half-lives of [omega]-OAH and [omega]-LAH in the presence of 40 [mu]M
17-ODCYA were 23 and 41 min, respectively. Inhibition of oleic acid
[omega]-hydroxylation was competitive with linoleic acid (18:2), but
noncompetitive with lauric acid (12:0). In contrast, oleic acid did not
inhibit [omega]-hydroxylation of lauric acid. Furthermore,
1-pentadecyltriazole inhibited [omega]-hydroxylation of oleic acid but not
of lauric acid. These results suggest that distinct monooxygenases catalyze
[omega]-hydroxylation of medium- and long-chain fatty acids in V. sativa
microsomes.