High-energy phosphate
From Wikipedia, the free encyclopedia
High-energy phosphate can mean one of two things:
- The phosphate-phosphate bonds formed when compounds such as adenosine diphosphate and adenosine triphosphate are created.
- The compounds that contain these bonds, which include the nucleoside diphosphates and nucleoside triphosphates, and the high-energy storage compounds of the muscle, the phosphagens. When people speak of a high-energy phosphate pool, they speak of the total concentration of these compounds with these high-energy bonds.
High-energy phosphate bonds are pyrophosphate bonds, acid anhydride linkages, formed by taking phosphoric acid derivatives and dehydrating them. As a consequence, the hydrolysis of these bonds is exothermic under physiological conditions, releasing energy.
| Reaction | ΔG [kJ/mol] |
|---|---|
| ATP + H2O → ADP + Pi | -36.8 |
| ADP + H2O → AMP + Pi | -36.0 |
| ATP + H2O → AMP + PPi | -40.6 |
| PPi → 2 Pi | -31.8 |
| AMP + H2O → A + Pi | -12.6 |
Except for PPi → 2 Pi, these reactions are, in general, not allowed to go uncontrolled in the human cell but are instead coupled to other processes needing energy to drive them to completion. Thus, high-energy phosphate reactions can:
- provide energy to cellular processes, allowing them to run;
- couple processes to a particular nucleoside, allowing for regulatory control of the process;
- drive the reaction to the right, by taking a reversible process and making it irreversible.
The one exception is of value because it allows a single hydrolysis, ATP + 2H2O → AMP + PPi, to effectively supply the energy of hydrolysis of two high-energy bonds, with the hydrolysis of PPi being allowed to go to completion in a separate reaction. The AMP is regenerated to ATP in two steps, with the equilibrium reaction ATP + AMP ↔ 2ADP, followed by regeneration of ATP by the usual means, oxidative phosphorylation or other energy-producing pathways such as glycolysis.
Often, high-energy phosphate bonds are denoted by the character '~'. In this notation, ATP becomes A-P~P~P.
[edit] References
- McGilvery, R. W. and Goldstein, G., Biochemistry - A Functional Approach, W. B. Saunders and Co, 1979, 345-351.
