Chemiosmotic Hypothesis

a hypothesis in biochemistry regarding the mechanism of the conversion of energy in biological membranes during the synthesis of adenosine triphosphate (ATP).

The chemiosmotic hypothesis was proposed by the British biochemist P. Mitchell in 1961 and further elaborated by him in 1966. According to the hypothesis, there exists a difference in electrical potentials and in the concentrations of hydrogen ions on a number of biological membranes, which Mitchell called coupled membranes (the internal membranes of mitochondria, chloroplasts, and the plasma membranes of bacteria). The difference in electrochemical potentials of hydrogen ions is due to the energy liberated during the activity of a chain of oxidation-reduction enzymes and is itself, in turn, the source of energy for the synthesis of ATP from adenosine diphosphate and inorganic phosphate. The formation of a difference in electrochemical potentials of hydrogen ions on the coupled membranes of mitochondria, chloroplasts, and certain bacteria can be considered proved.

In recent times it has been shown that the functions of the difference in electrochemical potentials of hydrogen ions are not limited to being the source of energy for the synthesis of ATP. For this reason, the chemiosmotic hypothesis has stimulated the study of the transport of ions and a number of biologically important molecules, such as amino acids and sugars, through the biological membrane. The hypothesis has also stimulated the study of the movement of bacteria and the regulation of the activity of membrane proteins.