Rat testosterone 7 alpha-hydroxylase. Isolation, sequence, and expression of cDNA and its developmental regulation and induction by 3-methylcholanthrene

J Biol Chem. 1987 Feb 25;262(6):2787-93.


A P-450, designated P-450a, with high testosterone 7 alpha-hydroxylase activity was purified from rat liver microsomes. Specific polyclonal antibody against this P-450 was used to screen a lambda gt11 expression cDNA library and a 1687-base pair cDNA was isolated and sequenced. The deduced protein had 492 amino acids, a calculated Mr of 56,016, and it shared 51 and 45% amino acid similarities to P-450e and P-450f, respectively. Regions of similarity were distributed in distinct areas of high and low similarity along the P-450a primary sequence. P-450a cDNA was introduced into yeast cells using the expression vector pAAH5, and the resultant yeast microsomes contained both a protein of identical electrophoretic mobility to that of rat P-450a and testosterone 7 alpha-hydroxylase activity. These results confirm enzyme reconstitution data and antibody inhibition data that P-450a possesses testosterone 7 alpha-hydroxylase activity. The antibody and cDNA probes were used to examine the mechanism of regulation of P-450a by inducers and during development. P-450a and its mRNA were present at low level in newborn rats and increased to maximal level at 1 week of age in both males and females. At age 12 weeks, however, the P-450a level decreased in males but remained elevated in females. Concomitant with the decrease in P-450a in adult males was an increase in level of another immunologically related P-450. In adult male rats, P-450a was induced almost 5-fold by administration of 3-methylcholanthrene and this induction was the result of an increase in its mRNA. These results establish testosterone 7 alpha-hydroxylase as a member of the P-450e gene family that is developmentally regulated, sex-dependent, and markedly inducible by 3-methylcholanthrene.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Aryl Hydrocarbon Hydroxylases*
  • Base Sequence
  • Cloning, Molecular
  • Cytochrome P-450 Enzyme System / biosynthesis
  • DNA / analysis*
  • Electrophoresis, Polyacrylamide Gel
  • Enzyme Induction
  • Isoenzymes / biosynthesis
  • Male
  • Methylcholanthrene / pharmacology*
  • Microsomes, Liver / enzymology
  • Rats
  • Rats, Inbred Strains
  • Steroid Hydroxylases / genetics
  • Steroid Hydroxylases / isolation & purification*


  • Isoenzymes
  • Methylcholanthrene
  • DNA
  • Cytochrome P-450 Enzyme System
  • Steroid Hydroxylases
  • Aryl Hydrocarbon Hydroxylases
  • testosterone 7-alpha-hydroxylase, hamster

Associated data

  • GENBANK/J02669