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P Ormos

Publications and source records attributed to P Ormos.

29 records · Page 2Linked to original sources
PubMed1987

Deprotonation of tyrosines in bacteriorhodopsin as studied by Fourier transform infrared spectroscopy with deuterium and nitrate labeling.

Fourier transform infrared (FTIR) difference spectra are presented for bacteriorhodopsin (BR) at low temperature. Previous FTIR measurements have identified several tyrosine residues that change their absorption characteristics between light-adapted BR and dark-adapted BR, or between intermediates K and M [Dollinger, G., Eisenstein, L., Lin, S.-L., Nakanishi, K., Odashima, K., & Termini, J. (1986) Methods Enzymol. 127, 649-662]. These changes were explained by protonation/deprotonation of tyrosine moieties and perturbation of the protein environment surrounding tyrosines. A tyrosine deprotonation was observed to occur between intermediates K and M. The present studies confine the deprotonation to being between intermediates L and M and show that no tyrosines undergo changes between the K and the L states. Evidence is presented that none of the tyrosines undergoing changes at low temperature can be assigned to tyrosine-64. The environmental changes of these tyrosines are discussed in relation to the proton pumping mechanism. Their spatial relation to the chromophore is also discussed. At least two tyrosines are suggested to reside close to the retinal binding site. The reactive groups of the nitrated tyrosine-64 are speculated to be remote from the Schiff base and the active tyrosines but can possibly interact sterically with the ionone ring of the retinal.

Bacteriorhodopsins↗
PubMed1987

Rebinding and relaxation in the myoglobin pocket.

The infrared stretching bands of carboxymyoglobin (MbCO) and the rebinding of CO to Mb after photodissociation have been studied in the temperature range 10-300 K in a variety of solvents. Four stretching bands imply that MbCO can exist in four substates, A0-A3. The temperature dependences of the intensities of the four bands yield the relative binding enthalpies and and entropies. The integrated absorbances and pH dependences of the bands permit identification of the substates with the conformations observed in the X-ray data (Kuriyan et al., J. Mol. Biol. 192 (1986) 133). At low pH, A0 is hydrogen-bonded to His E7. The substates A0-A3 interconvert above about 180 K in a 75% glycerol/water solvent and above 270 K in buffered water. No major interconversion is seen at any temperature if MbCO is embedded in a solid polyvinyl alcohol matrix. The dependence of the transition on solvent characteristics is explained as a slaved glass transition. After photodissociation at low temperature the CO is in the heme pocket B. The resulting CO stretching bands which are identified as B substates are blue-shifted from those of the A substates. At 40 K, rebinding after flash photolysis has been studied in the Soret, the near-infrared, and the integrated A and B substates. All data lie on the same rebinding curve and demonstrate that rebinding is nonexponential in time from at least 100 ns to 100 ks. No evidence for discrete exponentials is found. Flash photolysis with monitoring in the infrared region shows four different pathways within the pocket B to the bound substates Ai. Rebinding in each of the four pathways B----A is nonexponential in time to at least 10 ks and the four pathways have different kinetics below 180 K. From the time and temperature dependence of the rebinding, activation enthalpy distributions g(HBA) and preexponentials ABA are extracted. No pumping from one A substate to another, or one B substate to another, is observed below the transition temperature of about 180 K. If MbCO is exposed to intense white light for 10-10(3) s before being fully photolyzed by a laser flash, the amplitude of the long-lived states increases. The effect is explained in terms of a hierarchy of substates and substate symmetry breaking. The characteristics of the CO stretching bands and of the rebinding processes in the heme pocket depend strongly on the external parameters of solvent, pH and pressure. This sensitivity suggests possible control mechanisms for protein reactions.

Carbon Monoxide↗
PubMed1983

Displacement current on purple membrane fragments oriented in a suspension.

The displacement current is measured in a suspension of electric field-oriented purple membranes isolated from Halobacterium halobium, the photocycle being driven by a light flash. A simple quantitative theory of the method is presented and used to evaluate the distances the protons move during their way through the bacteriorhodopsin molecules. A lower limit of the velocity of proton movement is also given.

Bacteriorhodopsins↗
PubMed1983

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

The permanent dipole moment, polarizability, and the retinal angle of Halobacterium halobium purple membranes were determined at different pH values. All of the parameters have a maximum between pH 5 and 6. There is a reversal in the direction of the permanent dipole moment near pH 5. The value of permanent dipole moment was determined to be 60 D/protein at pH 6.6, and the value obtained for polarizability was 3 X 10(-28) Fm2/membrane fragment. The retinal angle of all-trans retinal was 0.8 degrees smaller than that of the 13-cis conformation.

Bacteriorhodopsins↗
PubMed1980

Photocurrent response of bacteriorhodopsin adsorbed on bimolecular lipid membranes.

The photo response of bacteriorhodopsin adsorbed on a bimolecular lipid membrane has been investigated using short-circuit current measurements. The results revealed a biphasic current vs. time curve for the photocurrent at pH values of approx. 7. This phenomenon could be modified by altering either the value of the external applied electrical field or the proton concentration differences. The observed effects of the external applied voltage, pH gradient and lipophilic proton carriers enabled us to conclude that the bacteriorhodopsin can be adsorbed in two different states, which give rise to a pumping effect and a flux of protons in opposite directions. A theoretical analysis of the photocycle in relation to the electrical field which acts on the proton uptake and release is proposed. The main effect of this field is to diminish the pumping rate due to the proton motive force resulting from the creation of space-charge in the vicinity of purple membrane fragments.

Bacteriorhodopsins↗
PubMed1980

Electric response of a back photoreaction in the bacteriorhodopsin photocycle.

The electric response of a back photoreaction in the bacteriorhodopsin photocycle was investigated. The proton pumping activity of green flash excited bacteriorhodopsin stops if the M412 form is illuminated by blue light (Karvaly and Dancsházy, 1977). In the present work a fast negative displacement current signal was measured in an oriented membrane suspension system, indicative of back movement of protons from M412 to BR570. Quantitative evaluation of the data shows that there are at least two steps in the back reaction, with different rate constants. The temperature dependence of the rate constants show simple linear Arrhenius behavior between 5 degree and 40 degree C. The rate constants were slower by a factor of 1.8 in D2O suspension. The relevance of the protein electric response signals (PERS) observed in this paper to the early receptor potential is discussed.

Bacteriorhodopsins↗
PubMed1978

Mechanism of generation and regulation of photopotential by bacteriorhodopsin in bimolecular lipid membrane.

Photoelectric properties of bacteriorhodopsin incorporated into a bimolecular lipid membrane were investigated with special regard to the mechanism of photoelectric field generation. It was shown that besides its proton pump and electric generator functions bacteriorhodopsin works as a possible molecular regulator of the light-induced membrane potential. When a bimolecular lipid membrane containing bacteriorhodopsin is continuously illuminated in its main visible absorption band, and afterwards by superimposed blue light matching the absorption band of the long-living photobleached bacteriorhodopsin (M412) as well, the latter either enhances or decreases the steady-state photoresponse, depending upon the intensity of the green light. Thus, the additional blue-light illumination tends to cause the resultant photoelectric membrane potential to become stabilized. Two alternative schemes are tentatively proposed for the photochemical cycle of bacteriorhodopsin whereby blue light can control photovoltage generation. A kinetic model of the proton pump and the regulation of the photoelectric membrane potential is presented. This model fits all the experimental findings, even quantitatively. From the model some kinetic and physical parameters of this light-driven pump could be determined.

Bacteriorhodopsins↗
PubMed1978

Investigation by focused laser beam scanning of the photoelectric activity of bacteriorhodopsin-containing lipid bilayers.

The photoelectric activity of different parts of lipid bilayer containing bacteriorhodopsin was investigated by moving a small actinic light spot across the Plateau-Gibbs border and the bimolecular part of this reconstituted model membrane. The results give direct evidence that bacteriorhodopsin incorporated into the bimolecular region of the lipid membrane is responsible for the photoelectric activity of this system. A technique for scanning the photoelectric activity of a modified bimolecular lipid membrane is described in detail.

Bacteriorhodopsins↗
PubMed1971

[Not Available].

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History, Modern 1601-↗
PubMedDate not supplied

Introduction of a method for three-dimensional mapping of the charge motion in bacteriorhodopsin.

Electric signals associated with the photocycle of bacteriorhodopsin carry valuable information about the proton transport process. Photocurrents measured by different experimental methods are interpreted in terms of intramolecular charge displacements. Permanent electrical asymmetry of the sample is considered to be a prerequisite for the detection of electric signals. The various photoelectric measuring techniques can be distinguished by the way of achievement of this asymmetry. A common feature of the available methods, however, is that the samples are cylindrically symmetric. Consequently, intramembraneous charge displacements can normally be monitored only along the axis of the membrane normal. We developed a novel method that allows also the detection of the in-plane components of the charge displacements. Samples containing oriented purple membrane fragments were used in the experiments, and the rotational symmetry was transiently broken via anisotropic excitation of the bR molecules by linearly polarized light. Kinetics of the normal and in-plane components were measured and interpreted as a result of spatial charge displacements associated with the proton transport process in bacteriorhodopsin.

Journal Article↗