Reaction catalyzed by 3(or 17)beta-hydroxysteroid dehydrogenase (1.1.1.51), 3beta-hydroxysteroid 3-dehydrogenase (1.1.1.270)

		+		NADPH	=			+		NADP+
	zymosterone	+		NADPH	=		zymosterol	+		NADP+