Address of the President Sir Andrew Huxley at the Anniversary Meeting, 30 November 1981

Abstract

The Copley Medal is awarded to Dr P. D. Mitchell, F. R. S., in recognition of his formulation and development of the chemiosmotic hypothesis that energy released through the oxidation of food or the capture of photons is conserved in a gradient of protons before being used in the synthesis of adenosine triphosphate. It has long been known that the oxidation of food materials takes place in subcellular organelles known as mitochondria and that these oxidations are somehow coupled to the synthesis of adenosine triphosphate (ATP) from adenosine diphosphate and free phosphate ions, ATP being the ‘fuel’ for almost all the activities – synthetic, contractile, secretory etc. – of the cell. It was generally assumed that all the steps leading to ATP synthesis were straightforward chemical reactions, but despite prolonged effort by biochemists the intermediate chemical events were not identified. Mitchell proposed that a key step was the storage of energy from the oxidations in a physico-chemical rather than a purely chemical form and that the event directly driven by the oxidations was the movement of hydrogen ions across an insulating mitochondrial membrane to create both a positive electric potential and an excess concentration of hydrogen ions on one side of the membrane. The synthesis of ATP is then driven by hydrogen ions moving down this electrochemical gradient, through appropriate enzymes inserted in the membrane.