Discrete species of activated oxygen yield different cytochrome P450 heme adducts from aldehydes.
Aldehydes are known to inactivate cytochrome P450 in the reconstituted enzyme system containing NADPH and NADPH-cytochrome P450 reductase under aerobic conditions in a mechanism-based reaction involving heme adduct formation [Raner, G. M., Chiang, E. W. , Vaz, A. D. N., and Coon, M. J. (1997) Biochemistry 36, 4895-4902]. In the study presented here, artificial oxidants were used to examine the mechanism of aldehyde activation by purified P450 2B4 in the absence of the usual O(2)-reducing system, and the adducts that were formed were isolated and characterized. With hydrogen peroxide as the oxidant, 3-phenylpropionaldehyde gives an adduct with a mass corresponding to that of native heme modified by a phenylethyl group, presumably arising from the reaction of a peroxy-iron species with the aldehyde to give a peroxyhemiacetal, which upon deformylation yields the alkyl radical. NMR analysis indicated that the substitution is specifically at the gamma-meso position. In contrast, with m-chloroperbenzoic acid as the oxidant, an adduct is formed from 3-phenylpropionaldehyde with a mass that is consistent with the addition of a phenylpropionyl group, apparently arising by hydrogen abstraction from the aldehyde to give the carbonyl carbon radical. m-Chloroperbenzoic acid by itself forms a heme adduct with a mass corresponding to the addition of a chlorobenzoyloxy group apparently derived from homolytic oxygen-oxygen bond cleavage. These and other results with nonanal and 2-trans-nonenal support the concept that this versatile enzyme utilizes discrete oxidizing species in heme adduct formation from aldehydes.
Kuo
C L
CL
Department of Biological Chemistry, Medical School, The University of Michigan, Ann Arbor 48109-0606, USA.
Raner
G M
GM
Vaz
A D
AD
Coon
M J
MJ
D000447:Aldehydes / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry* / Q000378:metabolism; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000737:chemistry / Q000378:metabolism; D008862:Microsomes, Liver / Q000201:enzymology; D019906:Nuclear Magnetic Resonance, Biomolecular; D016877:Oxidants / Q000737:chemistry / Q000378:metabolism; D011817:Rabbits; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013056:Spectrophotometry, Ultraviolet
D000447:Aldehydes; D016877:Oxidants; D017382:Reactive Oxygen Species; C013166:2-nonenal; C008664:nonanal; D006418:Heme; D003577:Cytochrome P-450 Enzyme System; C005556:propionaldehyde; D006861:Hydrogen Peroxide