Adenosine 5'-diphosphate (ADP) plays a central role in cellular energy transfer. It is a key intermediate in energy metabolism, primarily involved in the production of adenosine triphosphate (ATP), the main energy currency of the cell. When cells require energy, ATP is hydrolyzed to ADP, releasing energy for processes such as muscle contraction, nerve impulse propagation, and biosynthetic reactions. ADP can then be phosphorylated back to ATP through processes like oxidative phosphorylation in mitochondria and photosynthesis in chloroplasts, making it essential for sustained energy supply. In blood platelet function, ADP is stored in dense granules and released upon platelet activation. It binds to P2Y1 and P2Y12 receptors on platelet surfaces, promoting aggregation and thrombus formation. This makes ADP a critical mediator in hemostasis and a target for antiplatelet drugs used in treating cardiovascular diseases, such as clopidogrel, which blocks ADP binding to P2Y12 receptors. ADP is also used in biochemical assays and research settings to study enzyme kinetics, particularly in reactions involving kinases and ATP-dependent enzymes. It serves as a substrate or inhibitor in metabolic pathways, helping scientists understand cellular regulation and energy dynamics.