Adenosine kinase (AK) catalyzes the phosphorylation of ribofuranosyl-containing nucleoside analogues at the 5'-hydroxyl using ATP or GTP as the phosphate donor.The physiological function of AK is associated with the regulation of extracellular adenosine levels and the preservation of intracellular adenylate pools. Adenosine kinase is involved in the purine salvage pathway.