All living cells are sounded by a lipid bilayer which forms the cell membrane and separates the aqueous intraand extra cellular compartments. The lipid bilayer itself creates a five nanometer thick environment which is hydrophobic at its center and hydrophilic where it meets the bounding environments (Fig1). As throughout the rest of the cell, the membrane contains a repertoire of proteins whic...

The purple membrane (PM) is a specialized membrane patch found in halophilic archaea, containing the photoreceptor bacteriorhodopsin (bR). It is long known that calcium ions bind to the PM, but their position and role remain elusive to date. Molecular dynamics simulations in conjunction with a highly detailed model of the PM have been used to investigate the stability of calcium ions placed at ...

Spin-dependent photoluminescence (PL) quenching of CdSe nanoparticles (NPs) has been explored in the hybrid system of CdSe NP purple membrane, wild-type bacteriorhodopsin (bR) thin film on a ferromagnetic (Ni-alloy) substrate. A significant change in the PL intensity from the CdSe NPs has been observed when spin-specific charge transfer occurs between the retinal and the magnetic substrate. Thi...

The effects of charged groups of rhodopsin and bacteriorhodopsin on the potential energy surface of their chromophore are examined, taking into account the protein dielectric effect. It is found that the barriers for twisting double bonds of an isolated chromophore can be drastically reduced when the chromophore interacts with the protein charges. New types of local minima are found in the grou...

Bacteriorhodopsin of halobacterial purple membranes exhibits conformational flexibility in high electric field pulses (1-30 x 10(5) V m(-1), 1-100 micros). High-field electric dichroism data of purple membrane suspensions indicate two kinetically different structural transitions within the protein; involving a rapid (approximately 1 micros) concerted change in the orientation of both retinal an...

We have investigated the orientation of isolated fragments of Halobacterium halobium purple membrane (PM) adsorbed to poly-L-lysine-treated glass (PL-glass), by quanitative electron microscopy. Three lines of evidence support the conclusion that the cytoplasmic side of the membrane is preferentially absorbed. First, monolayer freeze-fracture reveals nonrandom orientation; more fracture faces (8...

Halobacterium halobium spheroplasts synthesize and accumulate a bacteriorhodopsin precursor. By labeling of the precursor with [35S]Met and [3H]Leu followed by Edman degradation, we have confirmed the previous conclusion from the DNA sequencing that the precursor contains 13 additional amino acids at the NH2 terminus of bacteriorhodopsin. Although not processed in the spheroplasts, it integrate...

Bacteriorhodopsin (BR) essentially free of native lipids has been prepared in a highly stable state. Purple membrane was solubilized in Triton X-100 and BR was purified by size exclusion chromatography using 3-[cholamidopropyl)dimethylammonio]-2-hydroxyl-1-propanesulfonic acid (CHAPSO) detergent at pH 5. Molar ratios of phospholipid/BR ranged from 0.4 to 0.05 corresponding to 94-98% phospholipi...