Adenosine kinase (ADK) phosphorylates adenosine and other related nucleosides [PMID:8577746, PMID:8917457]. It is exclusive to eukaryotes [PMID:9070863] and is a key enzyme in the purine salvage pathway. ADK catalyses the reaction:

This reaction prevents toxic levels of adenosine building up within the cell. Experiments have been carried out on Gallus gallus (chicken) embryonic neurons to document the toxicity of adenosine, and the associated requirement for ADK [PMID:9654340].

Adenosine and ATP have been connected with pain, and the control of pain [ISSN:0272-4391, PMID:9650842]. Associated with this, adenosine has also been shown to have a number of anti-inflammatory activities [ISSN:0272-4391]. Human ADK bears little sequence similarity to other mammalian nucleoside kinases, but does share high similarity with some microbrial ribokinases and fructokinases, suggesting possible evolutionary connections [PMID:8577746, PMID:8917457].