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

Barabás, Klára; Dér, András; Dancsházy, Zsolt; Ormos, Pál; Keszthelyi, L.; Marden, Michael C.

doi:10.1016/s0006-3495(83)84317-3

Cited by 71 publications

(55 citation statements)

References 16 publications

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“…This fact gave us the chance to derive a characteristic magnetic susceptibility value of pm, determined from the initial slope of the curve according to (1): ZI -Z2 = 7.41 x 10 -`,2 J/T 2. When calculating with the average membrane size, this susceptibility corresponds to an average molar value (per tool bR) of 1.68 x 10-: J/ (mol×T2), which reasonably supports previous results (1.2 x 10 -2 J/(mol x T2)) [8], taking into account the effect of membrane size distribution [6].…”

Section: Resultssupporting

confidence: 89%

“…The gel technique has the advantage that the resulting preparations are very stable, the medium can be changed repeatedly, and simultaneous electrical and optical measurements are easily accomplished [5]. The sustained application of an electric field necessary during polymerization, however, decreases orientation of pm because of electrophoretic disordering effects [6]. The poor orientation becomes a serious problem, when photoelectric signals of bR must be measured under extreme conditions, such as very high ionic strengths.…”

Section: Introductionmentioning

confidence: 99%

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Orientation of purple membrane in combined electric and magnetic fields

et al. 1995

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The orientation of purple membrane in gels for photoelectric measurements is relatively poor, when they are prepared with the standard technique of applying a DC electric field and rapid polymerization. We have improved it by adding a high magnetic field (17.5 T) and increasing the viscosity of the membrane suspension. This process has resulted so far in a 3-fold increase of the photoelectric signals obtained. The magnetic susceptibility of purple membrane was determined.Key words': Bacteriorhodopsin; Orientation; Electric field: Magnetic field; Electrooptics; Photoelectric signal; Magnetic susceptibilityTo continue the work, we had to improve the technique and have tried a combination of electric and magnetic fields. Magnetic field also induces a parallel ordering of the membrane sheets [8], which can be maintained nearly perfectly during polymerization [9]. However, since the magnetic dipole in contrast to the electric is an induced dipole, the asymmetric membranes are randomly facing in opposite directions. We shall use the term alignment for this type of order. If, however, an orienting electric field acts on the membrane sheets, subsequent application of a high magnetic field should considerably improve the degree of orientation, and, afford larger photoelectric signals and a better signal-to-noise ratio. Materials and methods

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Section: Resultssupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Orientation of purple membrane in combined electric and magnetic fields

et al. 1995

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“…(The outer side has more space for charges and counterions.) Moreover, it is well-known that charge distribution asymmetry depends on pH and changes its sign around pH 5 [14]. Taking into account that the direction of proton pumping does not change with pH [14][15][16], the resulting asymmetry easily explains the pH dependence of the scattering kinetics.…”

Section: Discussionmentioning

confidence: 99%

Light scattering changes and protein distortion in the bacteriorhodopsin during the photocycle

Czégé

1988

FEBS Letters

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A change in light scattering was detected during the photoeycle of the purple membrane. A systematic study of the pH, viscosity and photoseleetion dependence of scattering kinetics is given. From the experimental data it follows that purple membranes are bent, depending on the pH, and that the extent of bending changes during the photocycle is due to the functional protein. A theoretical treatment is also given. The model explains all the experimental data and, as an important consequence, calls attention to the fact that exact kinetic measurements cannot be performed without immobilizing the purple membranes.

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“…The experiments described here require a suspension of pm with nearly perfect orientation, which cannot be achieved with a dc electric field alone, because in a high electric field two effects counteract orientation: (i) perturbation by an induced dipole moment, perpendicular to the permanent dipole moment and (ii) migration and a resulting shear of the membrane fragments because of the net electric charge of pm (12,21). A high magnetic field will align the membranes perfectly, but because the alignment is caused by an induced magnetic dipole, it cannot orient them facing in the same direction.…”

Section: Methodsmentioning

confidence: 99%

Interpretation of the spatial charge displacements in bacteriorhodopsin in terms of structural changes during the photocycle

Dér

Oroszi

Kulcsár

et al. 1999

Proc. Natl. Acad. Sci. U.S.A.

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We have recently introduced a method, made possible by an improved orienting technique using a combination of electric and magnetic fields, that allows the threedimensional detection of the intramolecular charge displacements during the photocycle of bacteriorhodopsin. This method generates electric asymmetry, a prerequisite for the detection of electric signal on the macroscopic sample, in all three spatial dimensions. Purple membrane fragments containing bacteriorhodopsin were oriented so that their permanent electric dipole moment vectors were perpendicular to the membrane plane and pointed in the same direction. The resulting cylindrical symmetry was broken by photoselection, i. e., by f lash excitation with low intensity linearly polarized light. From the measured electric signals, the threedimensional motion of the electric charge center in the bacteriorhodopsin molecules was calculated for the first 400 s. Simultaneous absorption kinetic recording provided the time-dependent concentrations of the intermediates. Combining the two sets of data, we determined the discrete dipole moments of intermediates up to M. When compared with the results of current molecular dynamics calculations, the data provided a decisive experimental test for selecting the optimal theoretical model for the proton transport and should eventually lead to a full description of the mechanism of the bacteriorhodopsin proton pump.Bacteriorhodopsin (bR) is an integral protein in the plasma membrane of Halobacterium salinarum (1). Upon light absorption, bR transports protons across the membrane, converting the photon energy into the energy of a proton electrochemical gradient (for recent reviews, see refs. 2 and 3). bR is a single small protein and is the simplest known active ion pump and biological light energy transducer. Consequently, it is a prototype system for studying the basic steps and rules of biological energy transduction. bR consists of the 23-kDa protein moiety and a retinal chromophore attached to the side chain of Lys-216 via a protonated Schiff base. The retinal is located about halfway through the membrane and sustains an angle of Ϸ70°with the membrane normal. Trimers of bR form twodimensional crystalline patches in the plasma membrane. These purple membrane fragments (pm) can be isolated as sheets of about 0.5-m diameter.

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

Cited by 71 publications

References 16 publications

Orientation of purple membrane in combined electric and magnetic fields

Orientation of purple membrane in combined electric and magnetic fields

Light scattering changes and protein distortion in the bacteriorhodopsin during the photocycle

Interpretation of the spatial charge displacements in bacteriorhodopsin in terms of structural changes during the photocycle

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