Kinetic solvent isotope effect in human P450 CYP17A1-mediated androgen formation: evidence for a reactive peroxoanion intermediate

J Am Chem Soc. 2013 Nov 6;135(44):16245-7. doi: 10.1021/ja4086403. Epub 2013 Oct 29.

Abstract

Human steroid hormone biosynthesis is the result of a complex series of chemical transformations operating on cholesterol, with key steps mediated by members of the cytochrome P450 superfamily. In the formation of the male hormone dehydroepiandrosterone, pregnenolone is first hydroxylated by P450 CYP17A1 at the 17-carbon, followed a second round of catalysis by the same enzyme that cleaves the C17-C20 bond, releasing acetic acid and the 17-keto product. In order to explore the mechanism of this C-C "lyase" activity, we investigated the kinetic isotope effect on the steady-state turnover of Nanodisc-incorporated CYP17A1. Our experiments revealed the expected small positive (~1.3) isotope effect for the hydroxylase chemistry. However, a surprising result was the large inverse isotope effect (~0.39) observed for the C-C bond cleavage activity. These results strongly suggest that the P450 reactive intermediate involved in this latter step is an iron-bound ferric peroxoanion.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Biocatalysis
  • Dehydroepiandrosterone / biosynthesis*
  • Deuterium Oxide / chemistry
  • Deuterium Oxide / metabolism*
  • Ferric Compounds / chemistry
  • Ferric Compounds / metabolism*
  • Ferrous Compounds / chemistry
  • Ferrous Compounds / metabolism*
  • Humans
  • Kinetics
  • Male
  • Solvents / chemistry
  • Solvents / metabolism
  • Steroid 17-alpha-Hydroxylase / metabolism*
  • Water / chemistry
  • Water / metabolism*

Substances

  • Ferric Compounds
  • Ferrous Compounds
  • Solvents
  • Water
  • Dehydroepiandrosterone
  • CYP17A1 protein, human
  • Steroid 17-alpha-Hydroxylase
  • Deuterium Oxide