Editing Adenosine triphosphate (section)

==Reactive aspects==
The hydrolysis of ATP into ADP and inorganic phosphate

:ATP{{sup|4-}}(aq) + {{chem2|H2O}}(l) = ADP{{sup|3-}}(aq) + HPO{{sub|3}}{{sup|2-}}(aq) + H{{sup|+}}(aq)

releases {{convert|20.5|kJ/mol}} of [[enthalpy]]. This may differ under physiological conditions if the reactant and products are not exactly in these ionization states.<ref>{{cite journal |last1=Gajewski |first1=E. |last2=Steckler |first2=D. |last3=Goldberg |first3=R. |title=Thermodynamics of the hydrolysis of adenosine 5′-triphosphate to adenosine 5′-diphosphate |journal=J. Biol. Chem. |volume=261 |issue=27 |pages=12733–12737 |year=1986 |doi=10.1016/S0021-9258(18)67153-4 |pmid=3528161 |doi-access=free }}</ref> The values of the free energy released by cleaving either a phosphate (P<sub>i</sub>) or a pyrophosphate (PP<sub>i</sub>) unit from ATP at [[standard state]] concentrations of 1&nbsp;mol/L at pH&nbsp;7 are:<ref>{{cite book |title=Biochemistry |last1=Berg |first1=Jeremy M. |last2=Tymoczko|first2= John L.|last3= Stryer|first3= Lubert |year=2007 |edition=6th |publisher=W.&nbsp;H. Freeman |location=New York, NY |isbn=978-0-7167-8724-2 |page=413}}</ref>

:ATP + {{chem|H|2|O}} → ADP + P<sub>i</sub> {{pad|1.5em}} Δ''G''°' = −30.5&nbsp;kJ/mol (−7.3&nbsp;kcal/mol)
:ATP + {{chem|H|2|O}} → AMP + PP<sub>i</sub> {{pad|1em}}Δ''G''°' = −45.6&nbsp;kJ/mol (−10.9&nbsp;kcal/mol)
These abbreviated equations at a pH near 7 can be written more explicitly (R = [[adenosine|adenosyl]]):
:[RO-P(O)<sub>2</sub>-O-P(O)<sub>2</sub>-O-PO<sub>3</sub>]<sup>4−</sup> + {{chem|H|2|O}} → [RO-P(O)<sub>2</sub>-O-PO<sub>3</sub>]<sup>3−</sup> + [HPO<sub>4</sub>]<sup>2−</sup> +  H<sup>+</sup>
:[RO-P(O)<sub>2</sub>-O-P(O)<sub>2</sub>-O-PO<sub>3</sub>]<sup>4−</sup> + {{chem|H|2|O}} → [RO-PO<sub>3</sub>]<sup>2−</sup> + [HO<sub>3</sub>P-O-PO<sub>3</sub>]<sup>3−</sup> +  H<sup>+</sup>

At cytoplasmic conditions, where the ADP/ATP ratio is 10 orders of magnitude from equilibrium, the Δ''G'' is around −57&nbsp;kJ/mol.<ref name=Nicholls/>

Along with pH, the free energy change of ATP hydrolysis is also associated with Mg<sup>2+</sup> concentration, from ΔG°' = −35.7&nbsp;kJ/mol at a Mg<sup>2+</sup> concentration of zero, to ΔG°' = −31&nbsp;kJ/mol at [Mg<sup>2+</sup>] = 5&nbsp;mM. Higher concentrations of Mg<sup>2+</sup> decrease free energy released in the reaction due to binding of Mg<sup>2+</sup> ions to negatively charged oxygen atoms of ATP at pH&nbsp;7.<ref>{{cite book |last1=Garrett |first1=Reginald H. |last2=Grisham |first2=Charles M. |edition=6th |date=2016 |title=Biochemistry |publisher=Cengage Learning |page=68 |isbn=978-1305577206}}</ref>

[[File:MgATP2-small.gif|thumb|This image shows a 360-degree rotation of a single, gas-phase [[magnesium]]-ATP chelate with a charge of −2. The anion was optimized at the UB3LYP/6-311++G(d,p) theoretical level and the atomic connectivity modified by the human optimizer to reflect the probable electronic structure.]]