Reaction catalyzed by 3alpha-hydroxysteroid 3-dehydrogenase (Si-specific) (1.1.1.50)

		+		NAD+	=			+		NADH
	ursodeoxycholic acid	+		NAD+	=		7alpha,12alpha-dihydroxy-5beta-cholan-3-one-24-oic acid	+		NADH