Reaction catalyzed by pepsin A (3.4.23.1)

		+			=		4-[(1S,2R)-1,2-dihydroxy-3-oxobutyl]benzonitrile
	4-formylbenzonitrile	+		1-hydroxypropan-2-one	=		4-[(1S,2R)-1,2-dihydroxy-3-oxobutyl]benzonitrile