Protein kinase activity of purified Leydig cells: low protein kinase activity causes impaired steroidogenesis by band two cells.

Using a 0-32% continuous metrizamide density gradient, interstitial cells could be separated into five distinct bands. Cells localized in bands 1 (B1), 2 (B2), and 3 (B3) were isolated and incubated for 1h with or without human chorionic gonadotropin (hCG). Both B2 and B3 cells responded to hCG with increased cyclic AMP formation, but only B3 cells produced significantly more testosterone. Protein kinase activity of B2 cells was found to be extremely low compared with B1 and B3 cells. Additional treatment of B3 cells with collagenase did not cause any change in protein kinase activity. These results indicate that decreased protein kinase activity may be responsible for impaired testosterone synthesis in B2 cells.