2.7.4.8	Ca2+	10% as effective as Mg2+	642684	
2.7.4.8	Ca2+	activation	642685, 642686	
2.7.4.8	Ca2+	no activator	642561, 642688	
2.7.4.8	Co2+	-	642685	
2.7.4.8	Co2+	activation	642687	
2.7.4.8	Co2+	can partially replace Mg2+	642561, 642690, 642694	
2.7.4.8	Co2+	less than 7% as effective as Mg2+	642684	
2.7.4.8	Fe2+	activation, 90% as effective as Mg2+	642684, 642694	
2.7.4.8	Fe2+	no activator	642685	
2.7.4.8	Fe3+	activation, less than 7% as effective as Mg2+	642684