High energy phosphate
Encyclopedia
High-energy phosphate can mean one of two things:
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 exergonic
under physiological conditions, releasing energy.
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:
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 "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. It emphasizes the special nature of these bonds. Stryer states:ATP is often called a high energy compound and its phosphoanhydride bonds are referred to as high-energy bonds. There is nothing special about the bonds themselves. They are high-energy bonds in the sense that free energy is released when they are hydrolyzed, for the reasons given above. Lipmann’s term “high-energy bond” and his symbol ~P (squiggle P) for a compound having a high phosphate group transfer potential are vivid, concise, and useful notations. In fact Lipmann’s squiggle did much to stimulate interest in bioenergetics..
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, as with the breaking of any bond, is an endergonic step (i.e., it absorbs energy, not releases it). The negative free energy change comes instead from the increased resonance stabilisation and solvation of the products relative to the reactants.
- The phosphate-phosphate bonds formed when compounds such as adenosine diphosphateAdenosine diphosphateAdenosine diphosphate, abbreviated ADP, is a nucleoside diphosphate. It is an ester of pyrophosphoric acid with the nucleoside adenosine. ADP consists of the pyrophosphate group, the pentose sugar ribose, and the nucleobase adenine....
and adenosine triphosphateAdenosine triphosphateAdenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
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 phosphagenPhosphagenThe phosphagens are energy storage compounds, also known as high-energy phosphate compounds, are chiefly found in muscular tissue in animals. They allow a high-energy phosphate pool to be maintained in a concentration range, which, if it all were ATP, would create problems due to the ATP consuming...
s. 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
Pyrophosphate
In chemistry, the anion, the salts, and the esters of pyrophosphoric acid are called pyrophosphates. Any salt or ester containing two phosphate groups is called a diphosphate. As a food additive, diphosphates are known as E450.- Chemistry :...
bonds, acid anhydride linkages, formed by taking phosphoric acid
Phosphoric acid
Phosphoric acid, also known as orthophosphoric acid or phosphoric acid, is a mineral acid having the chemical formula H3PO4. Orthophosphoric acid molecules can combine with themselves to form a variety of compounds which are also referred to as phosphoric acids, but in a more general way...
derivatives and dehydrating them. As a consequence, the hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
of these bonds is exergonic
Exergonic reaction
An exergonic reaction is a chemical reaction where the change in the Gibbs free energy is negative, indicating a spontaneous reaction. Symbolically, the release of Gibbs free energy, G, in an exergonic reaction is denoted as...
under physiological conditions, releasing energy.
| Reaction | ΔG [kJ/mol] |
|---|---|
| ATP + H2O → ADP + Pi | -36.8 |
| ADP + H2O → AMP Adenosine monophosphate Adenosine monophosphate , also known as 5'-adenylic acid, is a nucleotide that is used as a monomer in RNA. It is an ester of phosphoric acid and the nucleoside adenosine. AMP consists of a phosphate group, the sugar ribose, and the nucleobase adenine... + Pi | -36.0 |
| ATP + H2O → AMP + PPi | -40.6 |
| PPi + H2O → 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
Oxidative phosphorylation
Oxidative phosphorylation is a metabolic pathway that uses energy released by the oxidation of nutrients to produce adenosine triphosphate . Although the many forms of life on earth use a range of different nutrients, almost all aerobic organisms carry out oxidative phosphorylation to produce ATP,...
or other energy-producing pathways such as glycolysis
Glycolysis
Glycolysis is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+...
.
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
Fritz Albert Lipmann
Fritz Albert Lipmann FRS was a German-American biochemist and a co-discoverer in 1945 of coenzyme A. For this, together with other research on coenzyme A, he was awarded half the Nobel Prize in Physiology or Medicine in 1953 .Lipmann was born in Königsberg, Germany to a Jewish family.Lipmann...
, who first proposed ATP as the main energy transfer molecule of the cell, in 1941. It emphasizes the special nature of these bonds. 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, as with the breaking of any bond, is an endergonic step (i.e., it absorbs energy, not releases it). The negative free energy change comes instead from the increased resonance stabilisation and solvation of the products relative to the reactants.
Further reading
- McGilvery, R. W. and Goldstein, G., Biochemistry - A Functional Approach, W. B. Saunders and Co, 1979, 345-351.