ADP is the abbreviation for adenosine 5'-diphosphate, a molecule involved in energy transfer within cells and with regulation of clot formation in the blood. It consists of an adenine ring, a ribose sugar and two phosphate groups.
Adenosine 5'-diphosphate is formed when adenosine 5'-triphosphate (ATP) is hydrolyzed to form ADP plus a free phosphate group. This is a spontaneous or exergonic reaction which releases energy that the cell then uses to drive nonspontaneous reactions.
ADP also plays an important role in hemostasis, the normal process of blood coagulation to stop bleeding when an injury occurs. Platelets in the blood will stick to the walls of blood vessels when a vessel is injured. The platelets then release several chemicals — including ADP — to regulate the coagulation process. ADP causes additional platelets in the blood to change shape and stick aggressively to the growing clot, increasing its size and strength. ADP also induces fibrinogen fibers to stick to and reinforce the clot.