Tags: Enzyme.
Nucleoside-diphosphate kinases (NDKs also NDP Kinase (poly)nucleotide kinases and nucleoside diphosphokinases) are enzymes that catalyze the exchange of phosphate groups between different nucleoside diphosphates. NDK activities maintain an equilibrium between the concentrations of different nucleoside triphosphates such as for example when GTP produced in the citric acid (Krebs) cycle is converted to ATP.