UMP is converted to UTP in two successive phosphorylation reactions involving ATP. The first reaction is catalyzed by a nucleoside monophosphate kinase that can use cytidine monophosphate (CMP), dCMP, or UMP as substrate The second reaction is catalyzed by a broad specificity nucleoside diphosphate kinase. These two reactions are functionally isoergonic (PRINCIPLE 1 OF BIOENERGETICS). UTP reacts with glutamine in an ATP-dependent reaction to form cytidine triphosphate (CTP). The oxygen on C4 of UTP forms a hydroxyl group by enolization; the hydroxyl group is phosphorylated by ATP. Glutamine then donates its amide group. liberated by hydrolysis at the enzyme's active site, and phosphate is displaced (Figure 14-5). The reaction is not driven by the simple hydrolysis of ATP; rather ATP participates in the actual chemical transformation. The CTP synthetase reaction occurs with the loss of one high-energy bond and is exergonic and unidirectional.