The enzyme 3 -hydroxysteroid dehydrogenase/ isomerase (3 HSD) is required for the biosynthesis of all active steroid hormones. It exists as multiple isoforms in humans and rodents, each a product of a distinct gene. Two isoforms, 3 HSD I and II, are expressed in a tissue-specific manner in humans. 3 HSD I is the only isoform expressed in the placenta, where it is required for the biosynthesis o...
