Electrokinetic charge of the anesthetic-induced bR480 and bR380 spectral forms of bacteriorhodopsin

Irreversible temperature-induced changes in purple membranes studied by electrooptics

The thermal stability of purple membranes is studied by electric light scattering. Information on the polarization mechanisms is obtained. Incomplete recovery of the initial electric state (i.e., of permanent dipole moment, p( perpendicular), and electric polarizability, gamma(fast, ||)) after the membranes are heated at temperatures above 60 degrees C is revealed. Additional slow polarizability components, gamma(slow, perpendicular) and gamma(slow, ||), relaxing at different characteristic frequencies than the fast longitudinal polarizability gamma(fast, ||) appear in the temperature range where the order-disorder transition takes place. The slow polarizability gamma(slow, perpendicular) is probably connected with counterion displacement in the electrical double layer perpendicular to the disk plane. The results are important for understanding the polarization mechanisms and the origin of slow orienting moments.

Alkane derivative-bacteriorhodopsin interaction: proton transport and protein structure

The effects of alkane derivatives, 1-alcohols (ROH), aliphatic amine hydrochlorides (RNH(2).HCl) and sodium aliphatic carboxylates (ROONa), on the proton pumping activity of bacteriorhodopsin (bR) in a purple membrane have been examined. Photocurrents in bR in the purple membrane adsorbed onto polyester thin film were recorded before and after exposure to these test substances. The peak photocurrent in bR was reversibly suppressed by each substance. From the dose-response curve, the concentrations required to reduce the peak capacitive current by 50% were determined for each homolog and then the standard free energies per CH(2) for the adsorption of the alkane derivatives to the site of action were estimated: -3.13 kJ mol(-1) for ROH, -3.05 kJ mol(-1) for RNH(3)(+), and -2.95 kJ mol(-1) for ROO(-). The proton pumping activity of bR was mainly suppressed by the hydrophobic interaction with the additive. The relative potencies of the functional groups of the alkane derivatives were almost comparable between 1-octanol (C(8)OH) and octylamine hydrochloride (C(8)NH(3)(+)) and about 10 times less effective for sodium octanoate (C(8)OO(-)) than for others. The addition of C(8)OH or C(8)OO(-) changed the absorption spectra of bR with a maximum at 560 nm to the spectra of the intermediate state with a maximum at 480 nm, while the C(8)NH(3)(+) decreased the intensity of the 560 nm band only with no blue-shift by the 480 nm band. We conclude that the action of the alkane derivatives is nonspecific and directed to all organized purple membrane structures and that the binding sites of the ROH and ROO(-) are different from that of RNH(3)(+).

The quantitative analysis of three action modes of volatile anesthetics on purple membrane

We quantitatively assessed the spectroscopic changes of purple membrane in relation to the concentrations of a volatile anesthetic. As reported previously, volatile anesthetics show three modes of action on purple membrane. By using an anesthetic for which the concentration in solution could be determined spectroscopically and by applying modified analytical methods regarding the M-intermediate lifetime, we were able to clarify the quantitative relation between anesthetic concentration and each mode of action, a relation which in the past has only been described qualitatively. We also determined through the measurement of transient pH changes with pyranine that the proton pump efficiency per photochemical cycle in an action mode induced with low concentrations of anesthetic does not change from that of the native state. Moreover, we dynamically obtained the individual M-bacteriorhodopsin difference spectrum of each state at room temperature using our flash photolysis system equipped with a wavelength-tunable dye laser. These results demonstrated again that we should clearly distinguish different action modes of anesthetics according to their concentrations.

Binding of volatile anesthetics to purple membranes studied by X-ray diffraction

Volatile anesthetics, diiodomethane and trifluoroethyl iodide, acted on the purple membrane of Halobacterium halobium in two different modes depending on the concentration. At low concentration, the absorption maximum of bacteriorhodopsin shifted from 561 to 558 nm (BR558) and the M-intermediate of the photocycle decayed faster than the native one. Higher concentration induced a species absorbing maximally at 480 nm (BR480) and the long-lived M-intermediates. The X-ray study suggested that anesthetics bound specifically to the protein-lipid interfacial region within a trimer near the surface of membrane in BR558 and entered into the hydrophobic domain of the membrane in BR480.