Lipid inserted at a water/oil interface has been used as a model of biological membranes. The phototransfer of protons from water into octane by bacteriorhodopsin immobilized in an oil-in-water emulsion, containing phospholipids in octane and inorganic salt in water, was investigated. During irradiation by visible light, a reversible alkalinization of the water phase was detected. The effect was not inhibited by uncouplers. The means of natural immobilization of bacteriorhodopsin at the water/lipid interface has been examined, and it was shown that the action spectrum of the reaction is the same as that of light absorption by bacteriorhodopsin. It has been shown that bacteriorhodopsin can perform the direct light-dependent transfer of protons from water into octane. This rules out the formation of trilaminary structures, with a cavity localized between a bacteriorhodopsin sheet and the lipid monolayer (so-called "third" water). The phototransfer of protons (H+) induces the transport of anions (X-) from water into octane as H+ X- ionic pairs. Valinomycin was shown to be an effective inhibitor of light-induced change of pH in the emulsion. A mathematical model of bacteriorhodopsin functioning at the interface is proposed. This model explains the experimentally observed dependence of the pH shift as a function of chemical composition of the medium and concentration of salt, and the different pH relaxation rates both in the dark, and under illumination. The model also describes the dependence of the photoeffect on light intensity. The emulsion enzymology allows the examination of naturally immobilized membrane enzymes in conditions close to those found in native systems.
ASJC Scopus subject areas