Interfacial electric polarizability of purple membranes in solution

Abstract

An investigation of the scattered light (lambda = 632.8 nm) from purple membrane suspensions with different concentrations subjected to external AC and DC electric fields has been carried out. The electric pulses used were in the field strength range 0-3.2 X 10(4) Vm-1 and the frequency range 10 Hz-1 MHz, the pulse duration being less than or equal to 0.5 s. A concentration dependence of the relative changes in the scattered light intensity was obtained, the effect being positive on orienting the suspensions by an AC field at 1 and 10 kHz, and negative in the case of a DC field. The negative effects in the diluted samples decrease and turn positive as the strength of the field increases. The positive effects show the existence of an interfacial polarizability along the plane of the membrane, and the negative ones suggest the presence of a permanent dipole moment (p), perpendicular to the plane of the membrane. The values of gamma (induced polarizability) and p were found to be on the order of 10(-28)-10(-29) Fm2 and 10(-24) Cm, respectively. An explanation in terms of membrane aggregation for the observed dependence on concentration is given.

Heterogeneity based on bending of purple membrane containing bacteriorhodopsin

“…In the first two orientations, PM surface is perpendicular to the orienting electric field, whereas PM surface, in the third one, is parallel with the orienting field direction. This was in agreement with earlier electric dichroism studies [18–20]. It should be noted that the optimization of dielectric data has necessitated the introduction of such first dispersion due to the large dielectric loss exhibited by such large fragments like PMs.…”

Electro-optical measurements on aqueous suspension of purple membrane from Halobacterium halobium

“…induced dipoles were clearly shown by Kimura et al (1981) using linear dichroism and by Todorov et al (1982) using light-scattering measurements. Tsuji and Rosenheck (1979), Tsuji and Neumann (1981), and Druckmann and Ottolenghi ( 1981 ) ordered the pm with short pulses of high electric field and confirmed the results of Shinar et al (1977).…”

Electrooptical measurements on purple membrane containing bacteriorhodopsin mutants

“…Electric dichroism permits the observation of the orientation and alignment of membranes in suspension. Measurement of the absorption of light, polarized parallel or perpendicular to the direction of the applied electric fields, as a function of their strength furnishes data on the values of the permanent electric dipole moment (,u) and the polarizability (a) of the pm (Shinar et al, 1977;Keszthelyi, 1980Keszthelyi, , 1982Druckmann and Ottolenghi, 1981;Kimura et al, 1981;Tsuji and Neumann, 1981;Todorov et al, 1982;Otomo et al, 1986). The pH dependencies of the permanent dipole moment, the polar-izability and the angle of the retinal relative to the membrane normal (0), which can be determined from these measurements, have already been studied in the case of wild-type bR (Kimura et al, 1981;Barabas et al, 1983).…”