L. Keszthelyi - Academia.edu (original) (raw)

Papers by L. Keszthelyi

Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1990

Biophysical Journal, 1983

Photochemistry and Photobiology, 2009

Acta Physica Academiae Scientiarum Hungaricae, 1971

The investigation of γ spectra of the isobaric analogue resonances gives useful information about... more The investigation of γ spectra of the isobaric analogue resonances gives useful information about the structure of the nuclei. Our original aim was to look for isobaric analogue resonances in (p, γ) reactions on several nuclei, and to study the systematics of their γ spectra.

FEBS Letters, 1995

The orientation of purple membrane in gels for photoelectric measurements is relatively poor, whe... more 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.

A very fast component (life time 0.2 microsecond) was found in the flash-induced absorption chang... more 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.

FEBS Letters, 1988

Theoretical and new experimental arguments are given to explain the reversal of photoelectric sig... more Theoretical and new experimental arguments are given to explain the reversal of photoelectric signals from purple membranes oriented and immobilized in gel due to the presence of TEMED. The continuous current induced by continuous illumination demonstrates a photoelement-like behaviour, the polarity of which is reversed by TEMED. The data render the counterioncollapse mechanism highly questionable.

FEBS Letters, 1989

ABSTRACT Purple membranes oriented and immobilized in gel show charge transfer at pH 0.55 if the ... more ABSTRACT Purple membranes oriented and immobilized in gel show charge transfer at pH 0.55 if the pH is set by HCl. Current appears as laser flash driven transient and also as continuous current by quasi-continuous illumination. If the pH value 0.55 is set by H2SO4 continuous current is not observed. The results suggest that bacteriorhodopsin may pump chloride ions at low pH.

Journal of Photochemistry and Photobiology B: Biology, 1992

Halorhodopsin (hR)-containing, tween-washed membrane fragments were oriented by an electric field... more Halorhodopsin (hR)-containing, tween-washed membrane fragments were oriented by an electric field and immobilized in a polyaclylamide gel. Using this preparation, the photoelectric response of hR under various conditions was measured with a time resolution of 0.5 p.

Biophysical Journal, 1994

Reconstitution of the photoelectric responses involved in photosensory transduction in "blind" ce... more Reconstitution of the photoelectric responses involved in photosensory transduction in "blind" cells of Chlamydomonas reinhardtfi carotenoid-deficient mutants was studied by means of a recently developed population method. Both the photoreceptor current and the regenerative response can be restored by addition of all-trans-retinal, 9-demethyl-retinal, or dimethyl-octatrienal, while the retinal analogs prevented from 1 3-cis/trans isomerization, 1 3-demethyl-retinal and citral, are not effective. Fluence dependence, spectral sensitivity, and effect of hydroxylamine treatment on retinal-induced photoelectric responses are similar to those found earlier in green strains of Chiamydomonas, although an alternative mechanism of antenna directivity in white cells of reconstituted "blind" mutants (likely based on the focusing effect of the transparent cell bodies) leads to the reversed sign of phototaxis in mutant cells under the same conditions. The results obtained indicate that both photoreceptor current and and regenerative response are initiated by the same or similar rhodopsins with arhaebacterial-like chromophore(s) and prove directly the earlier suggested identity of the photoreceptor pigment(s) involved in photomotile and photoelectric responses in flagellated algae.

Biochemical and Biophysical Research Communications, 1987

A general behavior of bacteriorhodopsin in purple membranes from Halobacterium halobium has been ... more 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.

Proceedings of the National Academy of Sciences, 1982

Linear dichroism was measured during the photocycle of bacteriorhodopsin. The anisotropy of the s... more Linear dichroism was measured during the photocycle of bacteriorhodopsin. The anisotropy of the sample was produced by the photoselection method. The measurements on purple membrane fragments embedded in agar gel were performed at room temperature with 200-psec time resolution at several wavelengths in the 240-to 550-nm spectral region. The induced anisotropy of the retinal chromophore remained constant after the formation of the photocycle intermediate M. The anisotropy was also time independent at the characteristic peaks ofthe UV absorption change. These-experimental data suggest that the direction of the retinal transition dipole moment remains unchanged. Moreover, the affected aromatic protein side chains also do not show any rotational motion when they are in the perturbed or ground states during the photocycle. Our data render it possible to calculate the restricted range of sudden chromophore rotations that might be coupled to the appearance and decay of the M intermediate.

European Biophysics Journal, 2001

The eects of glycyl-glycine and bis-trispropane buers on the light-excited electric signals due t... more The eects of glycyl-glycine and bis-trispropane buers on the light-excited electric signals due to proton motion in the molecule were studied for the bacteriorhodopsin (bR) mutants D38R, D96N, E204Q, R227Q, D85N, D85T, R82Q/D85N, and D85N/D96N in purple membranes and for delipidated purple membrane containing the wild-type bR. The results show additional charge motion caused by the buers in all cases. Arrhenius parameters calculated from the temperature dependence of the dierence signals (with buer minus without buer) are similar to the parameters found for the wild-type bR in the case of these buers: the values of the activation enthalpies are mostly in the range 25±50 kJ/mol; all the activation entropies are negative. The results are evaluated with the cluster hypothesis outlined previously.

Biophysical Journal, 2006

The L intermediate of bacteriorhodopsin was excited, and its electrical response was measured. Tw... more The L intermediate of bacteriorhodopsin was excited, and its electrical response was measured. Two positive components were found in it with respect to the direction of proton pumping: an unresolved fast component, and a slower one (t ¼ 7 ms) of small amplitude. The fast component was assigned to a charge motion corresponding to reisomerization of the retinal moiety, whereas the slow one was attributed to charge rearrangements reestablishing the ground state. Because three x-ray crystallographic structures have recently been reported for the L intermediate, it seemed important to calculate the intramolecular dipole moment changes associated to bR/L for all three structures, so as to compare them with similar quantities determined from the electrical signals. The results are discussed in terms of amino acid side chains possibly contributing to the observed effect. We propose to use electrical signals as a verification tool for intermediate structures of the photocycle, and thus for molecular models of proton pumping.

Biophysical Journal, 1996

Electrooptical measurements on purple membrane containing the wild-type and 10 different bacterio... more Electrooptical measurements on purple membrane containing the wild-type and 10 different bacteriorhodopsin mutants have shown that the direction of the permanent electric dipole moment of all these membranes reverses at different pH values in the range 3.2-6.4. The induced dipole moment and the retinal angle exhibit an increased value at these pHs. The results demonstrate that the bacteriorhodopsin protein makes an important contribution to the electrooptical properties of the purple membrane.

The Journal of Physical Chemistry, 2007

... 13. Milano F, Dorogi M, Szebényi K, Nagy L, Maróti P, Váró G, Giotta L, Agostiano A, Trotta M... more ... 13. Milano F, Dorogi M, Szebényi K, Nagy L, Maróti P, Váró G, Giotta L, Agostiano A, Trotta M Enthalpy/entropy driven activation of the first interquinone electron transfer in bacterial photosynthetic reaction centers embedded in vesicles of physiologically important phospholipids ...