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Late events in the photocycle of bacteriorhodopsin mutant L93A.
- Source :
-
Biophysical journal [Biophys J] 2003 Jun; Vol. 84 (6), pp. 3848-56. - Publication Year :
- 2003
-
Abstract
- In the photocycle of bacteriorhodopsin (bR) from Halobacterium salinarum mutant L93A, the O-intermediate accumulates and the cycling time is increased approximately 200 times. Nevertheless, under continuous illumination, the protein pumps protons at near wild-type rates. We excited the mutant L93A in purple membrane with single or triple laser flashes and quasicontinuous illumination, (i.e., light for a few seconds) and recorded proton release and uptake, electric signals, and absorbance changes. We found long-living, correlated, kinetic components in all three measurements, which-with exception of the absorbance changes-had not been seen in earlier investigations. At room temperature, the O-intermediate decays to bR in two transitions with rate constants of 350 and 1800 ms. Proton uptake from the cytoplasmic surface continues with similar kinetics until the bR state is reestablished. An analysis of the data from quasicontinuous illumination and multiple flash excitation led to the conclusion that acceleration of the photocycle in continuous light is due to excitation of the N-component in the fast N<-->O equilibrium, which is established at the beginning of the severe cycle slowdown. This conclusion was confirmed by an action spectrum.
- Subjects :
- Adaptation, Physiological physiology
Adaptation, Physiological radiation effects
Cells, Cultured
Darkness
Dose-Response Relationship, Radiation
Halobacterium salinarum genetics
Lasers
Mutation
Photic Stimulation methods
Photobiology methods
Protons
Bacteriorhodopsins physiology
Bacteriorhodopsins radiation effects
Halobacterium salinarum radiation effects
Membrane Potentials physiology
Membrane Potentials radiation effects
Periodicity
Purple Membrane physiology
Purple Membrane radiation effects
Subjects
Details
- Language :
- English
- ISSN :
- 0006-3495
- Volume :
- 84
- Issue :
- 6
- Database :
- MEDLINE
- Journal :
- Biophysical journal
- Publication Type :
- Academic Journal
- Accession number :
- 12770890
- Full Text :
- https://doi.org/10.1016/S0006-3495(03)75112-1