The regulation of adenosine kinase (AK) activity has the potential to control intracellular and interstitial adenosine (Ado) concentrations. In an effort to study the role of AK in Ado homeostasis in the central nervous system, two iso-forms of the enzymewere cloned fromamouse brain cDNA library. Following overexpression in bacterial cells, the cor-responding proteins were purified to homogeneity.