Adenosine diphosphate (ADP), also known as adenosine pyrophosphate (APP), is an important organic compound in metabolism and is essential to the flow of energy in living cells.ADP is a purine ribonucleoside 5'-diphosphate having adenine as the nucleobase. It has a role as a human metabolite and a fundamental metabolite. It is an adenosine 5'-phosphate and a purine ribonucleoside 5'-diphosphate. It is a conjugate acid of an ADP(3-) and an ADP(2-).Adenosine 5'-(trihydrogen diphosphate). An adenine nucleotide containing two phosphate groups esterified to the sugar moiety at the 5'-position.