A mechanism for the light-driven proton pump of Halobacterium halobium

MITCHELL'S hypothesis of chemiosmotic coupling between redox reactions and ATP synthesis in membranes1 is supported by the finding of a light-driven proton pump in the purple membrane of Halobacterium halobium2–4. The purple membrane contains the protein bacteriorhodopsin in a crystalline array, with retinal as chromophore5,6. We propose here, on the basis of quantumchemical arguments and experimental observations, that the H. halobium proton pump may involve proton translocation through photoisomerisation of retinal about its 14–15 single bond.

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