Adenylate kinase (EC [http://enzyme.expasy.org/EC/2.7.4.3 2.7.4.3]) (also known as ADK or myokinase) is a phosphotransferase enzyme that catalyzes the interconversion of the various adenosine phosphates (ATP, ADP, and AMP).  By constantly monitoring phosphate nucleotide levels inside the cell, ADK plays an important role in cellular energy homeostasis.