Ovarian 3,β‐hydroxysteroid dehydrogenase/Δ5‐4‐isomerase of rainbow trout: Its cDNA cloning and properties of the enzyme expressed in a mammalian cell

Abstract
A cDNA clone encoding 3β-hydroxysteroid dehydrogenase/Δ5-4-isomerase (3β-HSD) was isolated from a cDNA library of rainbow trout ovarian thecal cells. Southern hybridization analysis of trout genomic DNA with the cDNA suggested the presence of a single gene encoding 3β-HSD in the rainbow trout showing a total genomic size of less than 4 kilobases (kb). The cDNA hybridized to a single species of mRNA isolated from rainbow trout ovaries; the 1.4 kb transcripts were most abundant in trout ovaries during the later stages of oogenesis. The trout 3β-HSD expressed in non-steroidogenic monkey kidney tumor (COS-1) cells showed a unique enzymatic 3β-HSD activity. Dehydroepiandrosterone was a more favoral substrate of the trout 3β-HSD than 17α-hydroxypregnenolone. Interestingly, the trout 3β-HSD expressed in COS-1 cells exhibited minimal ability to convert pregnenolone to progesterone.

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