Steroid hydroxylation by human fetal CYP3A7 and human NADPH-cytochrome P450 reductase coexpressed in insect cells using baculovirus

Res Commun Mol Pathol Pharmacol. 1998 Apr;100(1):15-28.


Human fetal CYP3A7 and human NADPH-cytochrome P450 reductase were coexpressed in insect cells, TN-5, infected with a recombinant baculovirus carrying both cDNAs. The expression of reductase in TN-5 cells was shown to be sufficient for the CYP3A7 dependent 16 alpha-hydroxylation of dehydroepiandrosterone. However, the extra addition of cytochrome b5 and phospholipid was necessary to obtain a maximal activity of CYP3A7 catalyzing the reaction. CYP3A7 expressed in TN-5 cells was capable of metabolizing testosterone, cortisol and dehydroepiandrosterone 3-sulfate as well as dehydroepiandrosterone. The apparent Vmax for 6 beta-hydroxylations of testosterone was similar to that obtained for 6 beta-hydroxylation of cortisol (2.9 versus 2.5 nmol/nmolP450/min). In contrast, the apparent Vmax for 16 alpha-hydroxylation of dehydroepiandrosterone and its 3-sulfate were 20 and 2 times greater than those observed for steroid 6 beta-hydroxylations, respectively (67.5 and 5.8 versus 2.5-2.9 nmol/nmol P450/min). On the other hand, the apparent K(m) for 6 beta-hydroxylations of testosterone and cortisol were greater than those for 16 alpha-hydroxylations (120 and 860 versus 46-58 microM). Thus, CYP3A7 was active for steroid 6 beta-hydroxylations and 16 alpha-hydroxylations, but there were greater differences in Vmax/K(m) ratios between these reactions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Aryl Hydrocarbon Hydroxylases*
  • Baculoviridae / genetics*
  • Cytochrome P-450 CYP2C8
  • Cytochrome P-450 CYP2C9
  • Cytochrome P-450 CYP3A
  • Cytochrome P-450 Enzyme System / metabolism*
  • Dehydroepiandrosterone / metabolism
  • Genetic Vectors
  • Humans
  • Hydrocortisone / metabolism
  • Hydroxylation
  • Insecta / metabolism*
  • Kinetics
  • Microsomes / enzymology
  • NADPH-Ferrihemoprotein Reductase / biosynthesis
  • NADPH-Ferrihemoprotein Reductase / metabolism*
  • Protein Biosynthesis
  • Steroid 16-alpha-Hydroxylase
  • Steroids / metabolism*
  • Testosterone / metabolism


  • Steroids
  • Testosterone
  • Dehydroepiandrosterone
  • Cytochrome P-450 Enzyme System
  • CYP2C9 protein, human
  • Cytochrome P-450 CYP2C9
  • Aryl Hydrocarbon Hydroxylases
  • CYP2C8 protein, human
  • CYP3A7 protein, human
  • Cytochrome P-450 CYP2C8
  • Cytochrome P-450 CYP3A
  • Steroid 16-alpha-Hydroxylase
  • NADPH-Ferrihemoprotein Reductase
  • Hydrocortisone