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 halobium ^2-4. The purple membrane contains the protein bacteriorhodopsin in a crystalline array, with retinal as chromophore^5,6. 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.