Adenosine kinase (ADK) is a highly conserved enzyme that plays a crucial role in regulating intracellular adenosine levels by catalyzing the phosphorylation of adenosine to adenosine monophosphate (AMP) using ATP as a substrate. This enzyme is involved in various biological processes, including energy metabolism, protein phosphorylation networks, and the transmethylation pathway, which is essential for DNA methylation. ADK also has implications in several pathologies such as epilepsy, diabetes, and cancer due to its role in modulating adenosine receptor activation and influencing the balance of methylation reactions.