Cytidine triphosphate is a pyrimidine nucleoside triphosphate. CTP is a substrate in the synthesis of RNA. CTP is a high-energy molecule similar to ATP, but its role as an energy coupler is limited to a much smaller subset of metabolic reactions. CTP is a coenzyme in metabolic reactions like the synthesis of glycerophospholipids and glycosylation of proteins. CTP acts as an inhibitor of the enzyme Aspartate carbamoyltransferase, which is used in pyrimidine biosynthesis.