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1 Proton gradients

The proton gradient can be used as an intermediate energy storage for heat production and flagellar rotation . Additionally it is an interconvertible form of energy in active transport, electron potential generation, NADPH synthesis and ATP synthesis/hydrolysis.

Some archaea, most notably halobacteria, make proton gradients by pumping in protons from the environment with the help of the solar driven enzyme bacteriorhodopsin, here it is used for driving the molecular motor enzyme ATP synthase to make the necessary conformational changes required to synthesize ATP.

Proton gradients are also be made by bacteria by running ATP synthase in reverse, this is used to drive flagellas.

The F₁F_O ATP synthase is a reversible enzyme. Large enough quantities of ATP cause it to create a transmembrane proton gradient, this is used by fermenting bacteria which do not have an electron transport chain, and hydrolyze ATP to make a proton gradient, which they use for flagella and transport of nutrients into the cell.

In respiring bacteria under physiological conditions, ATP synthase generally runs in the opposite direction, creating ATP while using the protonmotive force created by the electron transport chain as a source of energy. The overall process of creating energy in this fashion is termed oxidative phosphorylationOxidative phosphorylation is a biochemical process in cells. It is the final metabolic pathway of cellular respiration, after glycolysis and the citric acid cycle. The process takes place at a biological membrane. In prokaryotes this is the plasma membran. Same process takes place in mitochondria, were ATP synthase is located in the inner mitochondrial membrane (so that F₁-part sticks into mitochondrial matrix, were ATP synthesis takes place).

2 See also

• Transmembrane potential differenceTransmembrane potential difference is the electrical potential difference across a plasma membrane. A graded potential is a gradient of transmembrane potential difference. The Ionic Basis of the Membrane Potential Cells are surrounded by a plasma membrane