Characterization of the guinea pig 3β-hydroxysteroid dehydrogenase/Δ5-Δ4-isomerase expressed in the adrenal gland and gonads

The guinea pig adrenal gland, analogous to the human, possesses the capacity to synthesize C19 steroids. In order to further understand the control of guinea pig adrenal steroidogenesis we undertook the characterization of the guinea pig 3β-hydroxysteroid dehydrogenase/Δ5-Δ4-isomerase (3β-HSD) expressed in the adrenal gland. A cDNA clone encoding guinea pig 3β-HSD isolated from a guinea pig adrenal library is predicted to encode a protein of 373 amino acid residues and 41,475 Da. Ribonuclease protection assay suggests that this cDNA corresponds to the predominant, if not the sole, mRNA species detectable in total RNA from the guinea pig adrenal gland, ovary and testis. The guinea pig 3β-HSD shows a similar affinity for both pregnenolone and dehydroepiandrosterone, and in addition, a 17β-HSD type II-like activity was also observed. A phylogenetical analysis of the 3β-HSD gene family demonstrates that the guinea pig is in a parallel branch to the myomorpha group supporting the hypothesis that the guinea pig lineage has branched off after the divergence among primates, artiodactyls and rodents, suggesting the paraphyly of the order rodentia.