 ATP consists of adenosine – composed of an adenine ring and a ribose sugar – and three phosphate groups ( triphosphate ) . The phosphoryl groups , starting with the group closest to the ribose , are referred to as the alpha ( α ) , beta ( β ) , and gamma ( γ ) phosphates . Consequently , it is closely related to the adenine nucleotide , a monomer of RNA . ATP is highly soluble in water and is quite stable in solutions between pH 6 @.@ 8 and 7 @.@ 4 , but is rapidly hydrolysed at extreme pH . Consequently , ATP is best stored as an anhydrous salt . 
