Mechanisms of energy conservation in the mitochondrial membrane.

Abstract

The importance of the inner mitochondrial membrane for respiratory chain-linked energy conservation is well recognized. The precise role of the membrane in the process, however, is not known. A problem of great current interest in this context concerns the mode of interaction of the mitochondrial electron-transport and ATPase systems in catalysing oxidative phosphorylation. According to the chemiosmotic hypothesis1 this interaction is indirect and involves as an obligatory intermediate a proton gradient across the membrane. In contrast, the chemical hypothesis of oxidative phosphorylation envisages the formation of high-energy intermediates as functional links between the two systems,2 possibly with the involvement of conformational changes of proteins3 and localized proton gradients.4 Since these intermediates most probably are of macromolecular nature, with only limited mobility within the membrane, such a mechanism would be likely to involve a direct interaction between the electron-transport and ATPase systems. Thus, whereas the chemiosmotic hypothesis considers the two systems as separate units, where each ATPase ought to be able to interact with any electron-transport chain within the same membrane (Fig. 1A), the chemical hypothesis is compatible with an assembly-like arrangement of the two systems, where any given ATPase may interact with only one electron-transport chain (Fig. 1B).