Structure and Expression of a New Complementary DNA Encoding the Almost Exclusive 3β-Hydroxysteroid Dehydrogenase/Δ5-Δ4-Isomerase in Human Adrenals and Gonads

The study identified and characterized a second type of cDNA clone, type II, encoding the 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta HSD) enzyme, which is crucial for steroid hormone formation. The type II cDNA was isolated from a human adrenal library and predicted to encode a protein with high homology to human placental type I and rhesus macaque ovary 3 beta HSD proteins. Experiments showed that type I protein had higher enzyme activity than type II, although both had equivalent specific activity. Ribonuclease protection assays revealed that type II transcripts were predominantly found in the human adrenal gland, ovary, and testis, while type I transcripts were mainly in the placenta and skin. This research demonstrated that adrenals and gonads express a distinct 3 beta HSD isoenzyme compared to the placenta.