Discrete species of activated oxygen yield different cytochrome P450 heme adducts from aldehydes

Biochemistry. 1999 Aug 10;38(32):10511-8. doi: 10.1021/bi9904712.

Abstract

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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Aldehydes / chemistry*
  • Aldehydes / metabolism
  • Animals
  • Cytochrome P-450 Enzyme System / chemistry*
  • Cytochrome P-450 Enzyme System / metabolism
  • Heme / chemistry*
  • Heme / metabolism
  • Hydrogen Peroxide / chemistry
  • Hydrogen Peroxide / metabolism
  • Microsomes, Liver / enzymology
  • Nuclear Magnetic Resonance, Biomolecular
  • Oxidants / chemistry
  • Oxidants / metabolism
  • Rabbits
  • Reactive Oxygen Species / metabolism*
  • Spectrophotometry, Ultraviolet

Substances

  • Aldehydes
  • Oxidants
  • Reactive Oxygen Species
  • 2-nonenal
  • nonanal
  • Heme
  • Cytochrome P-450 Enzyme System
  • propionaldehyde
  • Hydrogen Peroxide