Adenylate kinase (also known as ADK) is a phosphotransferase enzyme (EC 2.7.4.3) which catalyzes the production of ATP from ADP, a process involved in cellular energy homeostasis (see the "Biological homeostasis" section of "Homeostasis"). Specifically, the reaction catalyzed is: Phosphotransferase is a category of enzymes with the quality of catalyzing phosphorylation. ... Ribbon diagram of the catalytically perfect enzyme TIM. Factor D enzyme crystal prevents the immune system from inappropriately running out of control. ... EC numbers (Enzyme Commission numbers) are a numerical classification scheme for enzymes, based on the chemical reactions they catalyze. ... Homeostasis or homoeostasis is the property of an open system, especially living organisms, to regulate its internal environment so as to maintain a stable condition, by means of multiple dynamic equilibrium adjustments controlled by interrelated regulation mechanisms. ...

 2 ADP → ATP + AMP