![]() ![]() The hydrolysis of ATP into ADP and inorganic phosphate releases 20.5 kJ/mol of enthalpy. In the context of biochemical reactions, the P-O-P bonds are frequently referred to as high-energy bonds. Living cells maintain the ratio of ATP to ADP at a point ten orders of magnitude from equilibrium, with ATP concentrations fivefold higher than the concentration of ADP. At more extreme pHs, it rapidly hydrolyses to ADP and phosphate. The cycles of synthesis and degradation of ATP 2 and 1 represent input and output of energy, respectively.ĪTP is stable in aqueous solutions between pH 6.8 and 7.4, in the absence of catalysts. Salts of ATP can be isolated as colorless solids. The presence of Mg 2+ regulates kinase activity. Ī second magnesium ion is critical for ATP binding in the kinase domain. Due to the strength of the ATP-Mg 2+ interaction, ATP exists in the cell mostly as a complex with Mg 2+īonded to the phosphate oxygen centers. ![]() The binding of a divalent cation, almost always magnesium, strongly affects the interaction of ATP with various proteins. Binding of metal cations to ATP īeing polyanionic and featuring a potentially chelating polyphosphate group, ATP binds metal cations with high affinity. In neutral solution, ionized ATP exists mostly as ATP 4−, with a small proportion of ATP 3−. The three phosphoryl groups are labeled as alpha (α), beta (β), and, for the terminal phosphate, gamma (γ). In its many reactions related to metabolism, the adenine and sugar groups remain unchanged, but the triphosphate is converted to di- and monophosphate, giving respectively the derivatives ADP and AMP.
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