Emulsion Bioelectrochemistry: Bacteriorhodopsin Phototransfer of Protons through the Interface Water/Lipid in Octane

The interface of two immiscible liquids is widely used as a model biological membrane for investigation of fundamental processes of photosynthesis, biocatalysis, fusion and interaction of cells, elucidation of mechanisms of functioning of ionic pumps, and electron exchangers (Boguslavsky and Volkov, 1987). The bacteriorhodopsin sheets from Halobacterium halobium were one of the first membrane systems studied upon the octane/water interface (Boguslavsky et al., 1975, 1976; Boguslavsky and Volkov, 1987; Drachev et al., 1983; Hwang et al.,1977, Post et al.,1984). These studies were carried out in various laboratories, but the results itself as well as their interpretation significantly differed. The progress was achieved due to studies of (Post et al.,1984) who proposed the way to immobilize bacteriorhodopsin sheets in the system with extended surface, octane-in-water emulsion. In this case the control of phototransfer of protons was significantly simplified: the measurements of concentration of protons in aqueous medium of emulsion was carried out using the conventional pH-meter. In our opinion the emulsion system proposed in (Post et al., 1984) is quite promising, since it facilitates the quantitative examination of the transfer of various ions through the water/lipid interface during functioning of membrane ion pumps using the ion selective electrodes. The vast interfacial area makes it possible to obtain the products of heterogeneous reactions in macroscopic quantities, whereas the low dielectric constant of non-aqueous phase may result in a broad decrease of activation energy (Kharkats and Volkov, 1987). The emulsion enzymology enables one to study naturally immobilized membrane enzymes in conditions close to the native ones.