adenosine diphosphate (ADP)
Adenosine diphosphate (ADP) is a nucleotide consisting of adenine, the sugar D-ribose, and two phosphate groups. ADP is formed by the removal of one phosphate from an ATP molecule by enzymes called ATPases. The formation of ADP from ATP releases usable metabolic energy. ADP is converted back to ATP by ATP synthases. Thus ADP is an important energy transfer molecule in cells.