NADP-dependent oxidoreductase that has 20-alpha-hydroxysteroid dehydrogenase activity. Monomer. Detected in follicle granulosa cells (at protein level). Detected in heart, lung, liver, kidney, stomach, uterus, testis, skeletal muscle and granulosa cells of the follicle wall. Detected at low levels in preovulatory follicles. Up-regulated in preovulatory follicles during luteinization 12 to 36 hours after stimulation with human chorionic gonadotropin. Up-regulated in granulosa cells 12 to 39 hours after stimulation with human chorionic gonadotropin. Detected at low levels in corpora lutea. Detected at constant low levels in theca interna. Belongs to the aldo/keto reductase family.