2.5.1.9	Mg2+	absolute requirement	637579	
2.5.1.9	Mg2+	preferred cation	659720	
2.5.1.9	Mn2+	preferred cation	659720	
2.5.1.9	additional information	divalent cations are required for maximal activity	659720	
2.5.1.9	additional information	no effect by Ba2+, Co2+	637575