Light‐induced changes of the pH gradient and the membrane potential in H. halobium

The purple membrane of Halobacteria containing the retinal protein complex bacteriorhodopsin [ 1 ] was proposed to function as a light-driven proton pump [2,3]. Photophosphorylation mediated by bacteriorhodopsin has been observed under anaerobic conditions [4-61 and is best explained on the basis of the chemiosmotic hypothesis of Peter Mitchell [7]. Bacteriorhodopsin as an electrogenic p!oton pump creates transmembrane potentials and pH gradients in artificial systems such as liposomes and planar phospho lipid membranes [8-lo] . For the measurement of membrane potentials and pH gradients across bacterial cell membranes (e.g. S. faecalis) the distribution of lipophilic ions and weak acids (e.g. DMO) has been introduced [ 1 1 141. In this paper we report experiments demonstrating light-induced changes of the electrochemical proton gradient in intact cells of Halobacterium halobium.

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