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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 consists of three important structural components: a sugar backbone attached to adenine and two phosphate groups bonded to the 5 carbon atom of ribose .
ADP + P i → ATP (during anaerobic glycolysis and oxidative phosphorylation) When the phosphagen system has been depleted of phosphocreatine (creatine phosphate), the resulting AMP produced from the adenylate kinase (myokinase) reaction is primarily regulated by the purine nucleotide cycle .
The ATP-ADP translocase (also called adenine nucleotide translocase, ANT) is an antiporter and exchanges ADP and ATP across the inner membrane. The driving force is due to the ATP (−4) having a more negative charge than the ADP (−3), and thus it dissipates some of the electrical component of the proton electrochemical gradient.
ADP-ribosylation is the addition of one or more ADP-ribose moieties to a protein. [1] [2] It is a reversible post-translational modification that is involved in many cellular processes, including cell signaling, DNA repair, gene regulation and apoptosis. [3] [4] Improper ADP-ribosylation has been implicated in some forms of cancer. [5]
During aerobic respiration, ATP is synthesized in the mitochondrion by addition of a third phosphate group to adenosine diphosphate (ADP) in a process referred to as oxidative phosphorylation. ATP is also synthesized by substrate-level phosphorylation during glycolysis .
ATP is shown in red, ADP and phosphate in pink and the rotating γ subunit in black. This ATP synthesis reaction is called the binding change mechanism and involves the active site of a β subunit cycling between three states. [77] In the "open" state, ADP and phosphate enter the active site (shown in brown in the diagram).
At cytoplasmic conditions, where the ADP/ATP ratio is 10 orders of magnitude from equilibrium, the ΔG is around −57 kJ/mol. [12] Along with pH, the free energy change of ATP hydrolysis is also associated with Mg 2+ concentration, from ΔG°' = −35.7 kJ/mol at a Mg 2+ concentration of zero, to ΔG°' = −31 kJ/mol at [Mg 2+ ] = 5 mM.
The adenylate energy charge is an index used to measure the energy status of biological cells.. ATP or Mg-ATP is the principal molecule for storing and transferring energy in the cell : it is used for biosynthetic pathways, maintenance of transmembrane gradients, movement, cell division, etc...