Catalyzes the phosphorylation of the purine nucleoside adenosine at the 5' position in an ATP-dependent manner. Serves as a potential regulator of concentrations of extracellular adenosine and intracellular adenine nucleotides. adenosine + ATP = ADP + AMP + H(+) Binds 3 Mg(2+) ions per subunit. Activity is inhibited by 5-iodotubercidin and 5'-amino-5'-deoxyadenosine. Purine metabolism; AMP biosynthesis via salvage pathway; AMP from adenosine: step 1/1. Monomer. Widely expressed (PubMed:15317590). Highly expressed in liver, testis, kidney and spleen (at protein level). In brain, expression in most forebrain structures and the cerebellum is higher than in the midbrain and brainstem (at protein level) (PubMed:15317590). Major isoform in testis and kidney. Not detected in most brain regions, except in the cerebellum, where it is expressed at a similar level to that of isoform 2 (at protein level). Major isoform in spleen and in most brain regions, except in the cerebellum, where it is expressed at a similar level to that of isoform 1 (at protein level). Belongs to the carbohydrate kinase PfkB family.