Adenosine (ADO) is a purine nucleoside comprising a molecule of adenine attached to a ribose sugar molecule (ribofuranose) moiety via a β-N9-glycosidic bond. Adenosine 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 an inhibitory neurotransmitter, believed to play a role in promoting sleep and suppressing arousal.