2.7.7.44	Mg2+	best fulfills the requirement for a divalent cation, maximal activity of forward reaction at a Mg2+/UTP ratio of 2:1. In the reverse reaction below 5 mM diphosphate, a Mg2+:diphosphate ratio of approximately 1:1 gives optimal activity, excess of Mg2+ is inhibitory	6	
2.7.7.44	Mn2+	53% of the activation with Mg2+, excess of Mn2+ inhibits the reaction in both directions	11