2.4.1.56	Fe2+	activates, less effective than Mn2+	
2.4.1.56	Mg2+	activates, less effective than Mn2+	
2.4.1.56	Mn2+	-	
2.4.1.56	Mn2+	absolute requirement for divalent cations of which Mn2+ is most active, optimal concentration: 15 mM