When ATP is hydrolysed, it loses its terminal γ-phosphate group to form ADP and orthophosphate or inorganic phosphate (Pi).
ATP + H2O 
ADP + Pi
The standard free energy change ΔG° for this reaction is −7.3 Kcal/mol. Standard free energy changes have also been determined for the hydrolysis of other phosphorylated compounds or organophosphates. Under standard conditions, some phosphates yield more and some yield less free energy than ATP on hydrolysis. This intermediate position makes ATP to function as a high-energy compound. Two classes of organophosphates have been noticed in metabolism—enolphosphates (e.g., phosphoenolpyruvate) and phosphoguanidines (e.g., creatine phosphate, arginine phosphate).
Standard free energy of hydrolysis of some phosphorylated compounds is given in Table 7.1.
Table 7.1 Standard Free Energy of Hydrolysis of Some Phosphorylated Compounds
| DG′° | ||
|---|---|---|
| (kJ/mol) | (kcal/mol) | |
| Phosphoenolpyruvate | −61.9 | −14.8 |
| 1,3-bisphosphoglycerate (→ 3-phosphoglycerate + Pi) | −49.3 | −11.8 |
| Phosphocreatine | −43.0 | −10.3 |
| ADP (→ AMP + Pi) | −32.8 | −7.8 |
| ATP (→ ADP + Pi) | 30.8 | −7.3 |
| ATP (→ AMP + Pi) | 45.6 | −10.9 |
| AMP (→ adenosine+ Pi) | −14.2 | −3.4 |
| PPi (→ 2Pi) | −19.2 | −4.0 |
| Glucose 1-phosphate | −20.9 | −5.0 |
| Fructose 6-phosphate | −15.9 | −3.8 |
| Glucose 6-phosphate | −13.8 | −3.3 |
| Glycerol 1-phosphate | −9.2 | −2.2 |
| Acetyle-CoA | −31.4 | −7.5 |
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