High-energy phosphate can mean one of two things:
* The
phosphate
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid .
The phosphate or orthophosphate ion is derived from phosph ...
-phosphate (phosphoanhydride/phosphoric anhydride/macroergic/
phosphagen) bonds formed when compounds such as
adenosine diphosphate
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 backbo ...
(ADP) and
adenosine triphosphate
Adenosine triphosphate (ATP) is an organic compound that provides energy to drive many processes in living cells, such as muscle contraction, nerve impulse propagation, condensate dissolution, and chemical synthesis. Found in all known forms ...
(ATP) 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 usually
pyrophosphate
In chemistry, pyrophosphates are phosphorus oxyanions that contain two phosphorus atoms in a P–O–P linkage. A number of pyrophosphate salts exist, such as disodium pyrophosphate (Na2H2P2O7) and tetrasodium pyrophosphate (Na4P2O7), among o ...
bonds, acid
anhydride linkages formed by taking
phosphoric acid
Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solutio ...
derivatives and dehydrating them. As a consequence, the
hydrolysis
Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile.
Biological hydrolysis ...
of these bonds is
exergonic under physiological conditions, releasing
Gibbs free energy
In thermodynamics, the Gibbs free energy (or Gibbs energy; symbol G) is a thermodynamic potential that can be used to calculate the maximum amount of work (physics), work that may be performed by a closed system, thermodynamically closed system a ...
.
Except for PP
i → 2 P
i, 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 a reaction out of equilibrium (drive it ''to the right'') by promoting one direction of the reaction faster than the equilibrium can relax.
The one exception is of value because it allows a single hydrolysis, ATP + H
2O → AMP + PP
i, to effectively supply the energy of hydrolysis of two high-energy bonds, with the hydrolysis of PP
i 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
Oxidative phosphorylation (UK , US ) or electron transport-linked phosphorylation or terminal oxidation is the metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing chemical energy in order to produce adenosine t ...
or other energy-producing pathways such as
glycolysis.
Often, high-energy phosphate bonds are denoted by the character '~'. In this "squiggle" notation, ATP becomes A-P~P~P. The squiggle notation was invented by
Fritz Albert Lipmann, who first proposed ATP as the main energy transfer molecule of the cell, in 1941.
Lipmann's notation emphasizes the special nature of these bonds.
[Lubert Stryer ''Biochemsitry'', 3rd edition, 1988. Chapter 13, p. 318] Stryer states:
The term 'high energy' with respect to these bonds can be misleading because the negative free energy change is not due directly to the breaking of the bonds themselves. The breaking of these bonds, like the breaking of most bonds, is
endergonic and consumes energy rather than releasing it. The negative
free energy change comes instead from the fact that the bonds formed after hydrolysis - or the
phosphorylation
In chemistry, phosphorylation is the attachment of a phosphate group to a molecule or an ion. This process and its inverse, dephosphorylation, are common in biology and could be driven by natural selection. Text was copied from this source, ...
of a residue by ATP - are lower in energy than the bonds present before hydrolysis. (This includes ''all'' of the bonds involved in the reaction, not just the phosphate bonds themselves). This effect is due to a number of factors including increased
resonance stabilization and
solvation
Solvation (or dissolution) describes the interaction of a solvent with dissolved molecules. Both ionized and uncharged molecules interact strongly with a solvent, and the strength and nature of this interaction influence many properties of the ...
of the products relative to the reactants.
References
Further reading
* McGilvery, R. W. and Goldstein, G., ''Biochemistry - A Functional Approach'', W. B. Saunders and Co, 1979, 345–351.
* {{cite book , last1=Ferguson , first1=S. J. , last2=Nicholls , first2=David , last3=Ferguson , first3=Stuart , title=Bioenergetics 3 , publisher=Academic , location=San Diego, CA , year=2002 , isbn=978-0-12-518121-1 , edition=3rd, chapter=The myth of the 'high-energy phosphate bond'
Organophosphates
Pyrophosphates