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L Keszthelyi

Publications and source records attributed to L Keszthelyi.

At least 19 recordsLinked to original sources
PubMed1992

Bacteriorhodopsin: a picosecond optoelectric signal transducer.

This paper summarizes the results found in our laboratory investigating the ultrafast light-induced charge separation in bacteriorhodopsin. A special technique was elaborated for dried oriented samples of long term stability. An upper limit of 21 ps was found by a direct electric method for the early charge separation processes. A permanent electric field on the surface of illuminated samples was demonstrated. The potential application of such samples as ultrafast optoelectric signal transducers is discussed.

Bacteriorhodopsins↗
PubMed1991

Alternative translocation of protons and halide ions by bacteriorhodopsin.

Bacteriorhodopsin (bR568) in purple membrane near pH 2 shifts its absorption maximum from 568 to 605 nm forming the blue protein bRacid605, which no longer transports protons and which shows no transient deprotonation of the Schiff base upon illumination. Continued acid titration with HCl or HBr but not H2SO4 restores the purple chromophore to yield bRHCl564 or bRHBr568. These acid purple forms also regain transmembrane charge transport, but no transient Schiff base deprotonation is observed. In contrast to bR568, no rate decrease of the bRacidpurple transport kinetics is detected in 2H2O; however, the transport rate decreases by a factor of approximately 2 in bRHBr568 compared with bRHCl564. The data indicate that in the acid purple form bR transports the halide anions instead of protons. We present a testable model for the transport mechanism, which should also be applicable to halorhodopsin.

Anions↗
PubMed1990

Fast components of the absorption changes of bacteriorhodopsin at 275 nm and 296 nm.

A very fast component (life time 0.2 microsecond) was found in the flash-induced absorption changes of bacteriorhodopsin (bR) at 275 nm and 296 nm. This result was obtained by measuring the absorption changes at well defined delay times after the exciting laser flash (590 nm, 20 ns pulse duration). For this purpose a second laser flash was used as the monitoring beam. The very fast absorption changes of bR in the UV range are due to the rapid perturbation of the opsin moiety near the chromophore, as a result of the all-trans to 13-cis isomerization of the retinal taking place on the same time scale.

Absorption↗
PubMed1989

Transient spectroscopy of bacterial rhodopsins with an optical multichannel analyzer. 1. Comparison of the photocycles of bacteriorhodopsin and halorhodopsin.

We used a gated optical multichannel analyzer to measure transient flash-induced absorption changes in bacteriorhodopsin (BR) and halorhodopsin (HR) and developed criteria for calculating the absorption spectra of the photocycle intermediates and the kinetics of their rise and decay. The results for BR agree with data reported by a large number of other authors. The results for HR in the presence of chloride are consistent with earlier data and reveal an additional intermediate, not previously seen, in the submicrosecond time scale. Although an M412-like intermediate is not in the HR photocycle, a one-by-one comparison of the rest of the intermediates observed for BR and HR indicates a striking similarity between the photocycles of the two bacterial rhodopsins. This was previously not apparent, perhaps because the experimental approaches to the spectroscopy of the two pigments were different and the data were thus more fragmented.

Bacteriorhodopsins↗
PubMed1989

Charge motion in MbCO crystals after flash photolysis.

Charge motion accompanying the dissociation and recombination of carbon monoxide to oriented myoglobin crystals has been observed. The magnitude of the electrical signals detected after photodissociation by electrodes on either side of MbCO crystals of type A is consistent with the x-ray data showing that the doubly charged iron ion lies in the mean heme plane when a ligand is bound and moves out of the plane when deligated. Beyond 10 ms, the time development of the electrical signal is consistent with the kinetics observed optically after flash photolysis on the same crystals.

Carbon Monoxide↗
PubMed1988

The bacteriorhodopsin proton pump: effect of crosslinkings of lysine residues.

All six available lysine residues in bacteriorhodopsin were amidinated with dimethyl-3,3'-dithiobispropionimidate, which is a crosslinking agent. The photocycle was studied by measuring light absorption and electric signals. The data show an essential change in the photocycle: instead of single components, the rise of the signal due to the M intermediate can be decomposed into two components, and the decay into three. The life-times and the intensities of these components and in general the proton pumping activity of bacteriorhodopsin depend only negligibly upon pH. Changes upon removing the crosslinks are not significantly different from those in the crosslinked samples. The lysine residues therefore may not be considered of primary importance in proton translocation.

Bacteriorhodopsins↗
PubMed1988

Low temperature restriction of charge shift in the primary reaction of the bacteriorhodopsin photocycle.

Fast electrical signals associated with the primary photoreaction of the bacteriorhodopsin photocycle were studied on dried oriented samples in the temperature range from 77 to 300 K. The rise of the electrical signal, associated with bathointermediate formation, was faster than 5 ns even at 77 K; no slow rising component was detected at any temperature in the nano- to microsecond time range. The amplitude of the signal associated with bathointermediate formation was not affected by cooling from 300 to 210 K, but decreased by a factor of two when the sample was further cooled from 210 to 190 K. At 77 K the amplitude from the first excitation flash is 25-30 per cent of that at 260 K. Our data suggest that low temperature restricts the size of the charge shift during the bathointermediate formation, resulting in creation of a "low temperature bathointermediate" distinct from the "room temperature bathointermediate".

Bacteriorhodopsins↗
PubMed1987

Effect of cross linkers on the bacteriorhodopsin photocycle.

A general behavior of bacteriorhodopsin in purple membranes from Halobacterium halobium has been observed upon modification resulting in cross-linking of carboxyl and lysine groups. The rise of the M-intermediate contained two components with approximately 50-50% intensity; its decay showed three components with approximately 25-50-25% intensity respectively in a pH range of 5-9. The significance of these remarkably similar data with respect to the proton translocation mechanism in bacteriorhodopsin is that chemical modification allows us to conclude that disturbing parts of the hypothetical "proton conducting chain" does not inhibit proton translocation.

Bacteriorhodopsins↗
PubMed1987

Asymmetries of nature and the origin of biomolecular handedness.

New developments in the problem of the origin of the asymmetry of the living systems are reviewed. The time of the appearance of the asymmetry was very probably during the chemical evolution. The asymmetry of weak interaction is still considered small to be the cause of chiral purity. New sources of asymmetry should also be considered, like the one proposed by Gilat.

Biological Evolution↗
PubMed1986

Possibilities of biological energy production.

From the numerous possibilities of biological solar energy transduction the production of hydrogen was selected in our laboratory. There are two forms of H2 production: from biomass with enzymes (formate-hydrogen lyase and hydrogenase enzymes) and the exploitation of some living systems or their analogs to evolve H2 from water upon solar irradiation. To approach the first problem, a bacterial strain and a hydrogenase (H2ase) enzyme of good parameters were isolated. The system composed produced H2 from biomass with an energetic efficiency of 10-12 per cent. Dealing with the second task, by changing some environmental factors we succeeded to increase by a factor of 15 the quantity of H2 produced by Anabeana cylindrica from water in light. It is clear from these studies that further research is needed to understand better the mechanism and regulation of biological H2 production. The aim of this research is to utilize it as an economically feasible and environmentally harmless energy source.

Chromatiaceae↗
PubMed1985

Arrhenius parameters of the bacteriorhodopsin photocycle in dried oriented samples.

In dried oriented samples of purple membranes isolated from Halobacterium halobium the Arrhenius parameters of the photocycle showed an abrupt change at a water content of approximately 80 H2O molecules per bacteriorhodopsin molecule. This makes probable the existence of a water-dependent conformational change of the protein. This result underlines the importance of water in the proton-conduction mechanism inside the protein. The effect of the external electric potential on the rate constants of the photoelectric signals was also measured. The data demonstrate that the membrane potential affects the steps of the proton transport during the photocycle.

Bacteriorhodopsins↗
PubMed1984

Elemental analysis of samples of biological origin relative to their protein content by means of charged particle bombardment.

The particle-induced X-ray emission (PIXE) method and the 14N(d,p)15N nuclear reaction are combined for simultaneous trace element and nitrogen determination. Measurement of nitrogen content often allows the relating of the elemental concentrations determined by PIXE to the protein content of the sample. For the measurements only a small amount of sample material is needed; therefore, it is possible to keep track of the quantity of a certain element in the successive steps of a biomedical separation process. In about 10 min, trace element concentrations in the ppm range can be determined with a statistical accuracy of about 10%.

Cyanobacteria↗
PubMed1984

Coupling between the bacteriorhodopsin photocycle and the protonmotive force in Halobacterium halobium cell envelope vesicles. II. Quantitation and preliminary modeling of the M----bR reactions.

The cell membrane of Halobacterium halobium (H. halobium) contains the proton-pump bacteriorhodopsin, which generates a light-driven transmembrane protonmotive force. The interaction of the bacteriorhodopsin photocycle with the electric potential component of the protonmotive force has been investigated. H. halobium cell envelope vesicles have been prepared by sonication and further purified by ultracentrifugation on Ficoll/NaCl/CsCl density gradients. Under continuous illumination (550 +/- 50 nm) varied from 0 to 40 mW cm-2, the vesicles maintain a membrane potential of 0 to -100 mV. The membrane potential was measured by flow dialysis of 3H-TPMP+ uptake and could be abolished by the uncoupler carbonylcyanide-m-chlorophenylhydrazone. Time-resolved absorption spectroscopy was used to measure the decay kinetics of the M photocycle intermediate, which was initiated by a weak laser flash (588 nm), while the vesicles were continuously illuminated as above. The M decay kinetics were fitted with two exponential decays by a computer deconvolution program. The faster decaying form decreases in amplitude (70 to 10% of the total) and the slower decaying form increases in amplitude and lifetime (23 to 42 ms) as the background light intensity increases. Although any correlation between the membrane potential and the bacteriorhodopsin photocycle M-forms is complex, the present data will allow specific tests of the physical mechanism for this interaction to be designed and conducted.

Bacteriorhodopsins↗
PubMed1984

Temperature dependence of ATP release from "caged" ATP.

The ATP release from "caged" ATP by laser flash was determined at different temperatures and pH values. We measured the time resolved absorbance changes of the coloured intermediate, which is involved in the photolytic process. The linearity of the Arrhenius curves suppose only one process and the calculated activation enthalpies (around 55 kJ/mole) did not change markedly at the pH values of 6.0, 7.0 and 8.0

Adenosine Triphosphate↗
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↗