5′-Deoxy-5′-(methylthio)adenosine (Methylthioadenosine, MTA) is a naturally occurring sulfur-containing nucleoside produced by the decarboxylation of S-adenosylmethionine. This nucleoside is a potent agonist of adenosine receptors with Ki of 0.15, 1.13, 13.9, and 0.68 μM for A1, A2A, A2B, and A3, respectively.