Structural and Functional Relationships in the Adenylate Kinase Family

All cells make wide use of the adenine nucleotides AMP, ADP, and ATP to accept, store, and transfer chemical energy. The nucleotides are also essential as modulators of regulatory enzymes of glycolysis, of the citric acid cycle, and of oxidative phosphorylation. Consequently, all the factors affecting the concentrations of intracellular adenine nucleotides play important roles. One such factor is adenylate kinase (ATP: AMP phosphotransferase, EC 2.7.4.3, myokinase, AK), a ubiquitous small monomeric intracellular enzyme (Mr=20,000–26,000) that catalyzes the interconversion of the adenosine nucleotides according to Mg++ATP + AMP ⇌ Mg++ADP + ADP. The catalysis requires a divalent cation, preferentially Mg++ (Noda 1973).