Adenosine is a purine nucleoside composed of a molecule of adenine attached to a ribose sugar molecule (ribofuranose) moiety via a ß-N₉-glycosidic bond. Adenosine is widely found in nature and plays an important role in biochemical processes, such as energy transfer — as adenosine triphosphate (ATP) and adenosine diphosphate (ADP) — as well as in signal transduction as cyclic adenosine monophosphate (cAMP). It is also a neuromodulator, believed to play a role in promoting sleep and suppressing arousal. Adenosine also plays a role in regulation of blood flow to various organs through vasodilation.