Adenylate kinase (EC 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.The reaction catalyzed is:

Thus, the mitochondrion attempts to keep ATP levels high due to the combined action of adenylate kinase and the controls on oxidative phosphorylation.

[6] Two further enzymes are known to be related to the ADK family, i.e. yeast uridine monophosphokinase and slime mold UMP-CMP kinase.

It has been shown that the mutation R88G results in 99% loss of catalytic activity of this enzyme, suggesting that this residue is intimately involved in the phosphoryl transfer.

[8] Another highly conserved residue is Arg119, which lies in the adenosine binding region of the ADK, and acts to sandwich the adenine in the active site.

It has been suggested that the promiscuity of these enzymes in accepting other NTP's is due to this relatively inconsequential interactions of the base in the ATP binding pocket.

[9] A network of positive, conserved residues (Lys13, Arg123, Arg156, and Arg167 in ADK from E. coli) stabilize the buildup of negative charge on phosphoryl group during the transfer.

[9] Flexibility and plasticity allow proteins to bind to ligands, form oligomers, aggregate, and perform mechanical work.

This generated AMP can, for example, stimulate various AMP-dependent receptors such as those involved in glycolytic pathways, K-ATP channels, and 5' AMP-activated protein kinase (AMPK).

[15] It facilitates decoding of cellular information by catalyzing nucleotide exchange in the intimate “sensing zone” of metabolic sensors.

[15] Adenylate kinase is present in mitochondrial and myofibrillar compartments in the cell, and it makes two high-energy phosphoryls (β and γ) of ATP available to be transferred between adenine nucleotide molecules.

[15][16] In essence, adenylate kinase shuttles ATP to sites of high energy consumption and removes the AMP generated over the course of those reactions.

This reduces the energetic signal communication in the post-ischemic heart and precipitates inadequate coronary reflow following ischemia-reperfusion.

Enhanced growth and elevated photosynthetic amino acid is associated with plastidial adenylate kinase deficiency in Arabidopsis thaliana.