adenosine diphosphate (ADP)
A nucleotide consisting of adenine,
the sugar D-ribose, and two phosphate
groups. Adenosine diphosphate (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.