ABSTRACT
Rates of thermoinduced conformational transitions of reaction center (RC) complexes providing effective electron transport were studied in chromatophores and isolated RC preparations of various photosynthesizing purple bacteria using methods of fast freezing and laser-induced temperature jump. Reactions of electron transfer from the primary to secondary quinone acceptors and from the multiheme cytochrome c subunit to photoactive bacteriochlorophyll dimer were used as probes of electron transport efficiency. The thermoinduced transition of the acceptor complex to the conformational state facilitating electron transfer to the secondary quinone acceptor was studied. It was shown that neither the characteristic time of the thermoinduced transition within the temperature range 233-253 K nor the characteristic time of spontaneous decay of this state at 253 K exceeded several tens of milliseconds. In contrast to the quinone complex, the thermoinduced transition of the macromolecular RC complex to the state providing effective electron transport from the multiheme cytochrome c to the photoactive bacteriochlorophyll dimer within the temperature range 220-280 K accounts for tens of seconds. This transition is thought to be mediated by large-scale conformational dynamics of the macromolecular RC complex.
Subject(s)
Bacteria/metabolism , Bacteriochlorophylls/metabolism , Bacteriorhodopsins/metabolism , Electron Transport , Photosynthetic Reaction Center Complex Proteins/chemistry , Bacteria/chemistry , Bacteriochlorophylls/chemistry , Bacteriorhodopsins/chemistry , Cytochrome c Group/chemistry , Cytochrome c Group/metabolism , Kinetics , Lasers , Light , Light-Harvesting Protein Complexes , Oxidation-Reduction , Photosynthetic Reaction Center Complex Proteins/metabolism , Protein Conformation , TemperatureABSTRACT
A model of the last parts of the bacteriorhodopsin (bR) photocycle is proposed on the basis of experimental data for the kinetic behavior of the 'O' intermediate during a temperature pulse in distilled water suspension. The model includes the previously proposed (but not well characterized) intermediate 'N' between the 'M' and 'O' states of bR. This intermediate exists in fast temperature-dependent quasi-stationary equilibrium with the red-shifted intermediate 'O' and has a maximum of absorption close to the bR spectrum.
Subject(s)
Bacteriorhodopsins , Kinetics , Photochemistry , Spectrum Analysis , TemperatureABSTRACT
According to the changes of absorption spectra kinetics of two primary stages of bacteriorhodopsin photochemical cycle was studied in the temperature range 160 +/- 300 degrees K. It has been found that for K610-L550 transition in the range under study the rate-temperature relationship is described by Arrhenius law with the activation energy Ea = 0.68 eV. For L550-M412 transition Ea = 0.69 eV. The character of temperature relationship, of the rate and amplitude for this transition indicates that at T less than or equal to 270 degrees K a phase transition is possible.
