NME4, also known as nucleoside diphosphate kinase, mitochondrial, belongs to the NDK family. NME4 are ubiquitous enzymes that catalyze transfer of gamma-phosphates, via a phosphohistidine intermediate, between nucleoside and dioxynucleoside tri- and diphosphates. The enzymes are products of the nm23 gene family, which includes NME4. NME4 plays a major role in the synthesis of nucleoside triphosphates other than ATP.