The evolution of the light-induced absorption difference spectrum (380-500 nm) of the reaction ce... more The evolution of the light-induced absorption difference spectrum (380-500 nm) of the reaction centers from photosynthetic purple bacteria Rhodobacter sphaeroides has been examined over 200 µ s. The observed changes are interpreted as the effects of proton movement along the H-bond between the primary quinone acceptor and its protein surroundings. A theoretical analysis of the spectral evolution, considering the proton tunneling kinetics, corroborates this interpretation. The electronic state of the primary quinone is stabilized within tens of microseconds; the process is retarded upon deuteration of the reaction center as well as in 90% glycerol, and accelerated upon nondestructive heating to 40 ° C.
The kinetics of electron transfer between primary and secondary quinone acceptors of the photosyn... more The kinetics of electron transfer between primary and secondary quinone acceptors of the photosynthetic reaction center (RC) of the purple bacterium Rhodobacter sphaeroides wild type was studied at the wavelengths 400 and 450 nm. It was shown that removing of molecular oxygen from RC preparations slowed down the fast phase of the process from 4 4.5 µsec to tens of microseconds. Similar effects were observed after the incubation of RC in heavy water for 72 h or glycerol addition (90% v/v) to RC preparations. The observed effects are interpreted in terms of the influence of these agents on the hydrogen bond system of the RC. The state of this system can determine the formation of different RC conformations that are charac terized by different rates of electron transfer between quinone acceptors.
The evolution of the light-induced absorption difference spectrum (380-500 nm) of the reaction ce... more The evolution of the light-induced absorption difference spectrum (380-500 nm) of the reaction centers from photosynthetic purple bacteria Rhodobacter sphaeroides has been examined over 200 µ s. The observed changes are interpreted as the effects of proton movement along the H-bond between the primary quinone acceptor and its protein surroundings. A theoretical analysis of the spectral evolution, considering the proton tunneling kinetics, corroborates this interpretation. The electronic state of the primary quinone is stabilized within tens of microseconds; the process is retarded upon deuteration of the reaction center as well as in 90% glycerol, and accelerated upon nondestructive heating to 40 ° C.
The evolution of the light-induced absorption difference spectrum (380-500 nm) of the reaction ce... more The evolution of the light-induced absorption difference spectrum (380-500 nm) of the reaction centers from photosynthetic purple bacteria Rhodobacter sphaeroides has been examined over 200 µ s. The observed changes are interpreted as the effects of proton movement along the H-bond between the primary quinone acceptor and its protein surroundings. A theoretical analysis of the spectral evolution, considering the proton tunneling kinetics, corroborates this interpretation. The electronic state of the primary quinone is stabilized within tens of microseconds; the process is retarded upon deuteration of the reaction center as well as in 90% glycerol, and accelerated upon nondestructive heating to 40 ° C.
The effect of molecular oxygen on the temporary stabilization of an electron at the secondary qui... more The effect of molecular oxygen on the temporary stabilization of an electron at the secondary quinone acceptor (Q B ) of photosynthetic reaction centers (RC) of the purple bacterium Rhodobacter sphaeroides was studied in the preceding work [1]. In the absence of exogenous donors of an electron, photoactivation of pigment-pro tein complexes of RC isolated from chromatophore membranes of Rb. sphaeroides induces fast (characteristic time, ~200 psec) transfer of an electron from the pho toactive bacteriochlorophyll dimer (P) to the primary quinone acceptor (Q A ). Then, within about 200 µsec the electron is transferred to Q B . In the RC of Rb. sphaeroides, the two quinone acceptors are molecules of ubiquinone 10. In further dark reactions the electron returns back to oxidized P. Electrostatic stabilization of the electron in quinone acceptors of RC is due to proton displacement in the RC microenvironment. Changes in the charge state of quinone modify the pK value of the protonated amino acid residues of the RC protein located within the vicinity of 15 17 Å [2 4].
The evolution of the light-induced absorption difference spectrum (380-500 nm) of the reaction ce... more The evolution of the light-induced absorption difference spectrum (380-500 nm) of the reaction centers from photosynthetic purple bacteria Rhodobacter sphaeroides has been examined over 200 µ s. The observed changes are interpreted as the effects of proton movement along the H-bond between the primary quinone acceptor and its protein surroundings. A theoretical analysis of the spectral evolution, considering the proton tunneling kinetics, corroborates this interpretation. The electronic state of the primary quinone is stabilized within tens of microseconds; the process is retarded upon deuteration of the reaction center as well as in 90% glycerol, and accelerated upon nondestructive heating to 40 ° C.
The kinetics of electron transfer between primary and secondary quinone acceptors of the photosyn... more The kinetics of electron transfer between primary and secondary quinone acceptors of the photosynthetic reaction center (RC) of the purple bacterium Rhodobacter sphaeroides wild type was studied at the wavelengths 400 and 450 nm. It was shown that removing of molecular oxygen from RC preparations slowed down the fast phase of the process from 4 4.5 µsec to tens of microseconds. Similar effects were observed after the incubation of RC in heavy water for 72 h or glycerol addition (90% v/v) to RC preparations. The observed effects are interpreted in terms of the influence of these agents on the hydrogen bond system of the RC. The state of this system can determine the formation of different RC conformations that are charac terized by different rates of electron transfer between quinone acceptors.
The evolution of the light-induced absorption difference spectrum (380-500 nm) of the reaction ce... more The evolution of the light-induced absorption difference spectrum (380-500 nm) of the reaction centers from photosynthetic purple bacteria Rhodobacter sphaeroides has been examined over 200 µ s. The observed changes are interpreted as the effects of proton movement along the H-bond between the primary quinone acceptor and its protein surroundings. A theoretical analysis of the spectral evolution, considering the proton tunneling kinetics, corroborates this interpretation. The electronic state of the primary quinone is stabilized within tens of microseconds; the process is retarded upon deuteration of the reaction center as well as in 90% glycerol, and accelerated upon nondestructive heating to 40 ° C.
The evolution of the light-induced absorption difference spectrum (380-500 nm) of the reaction ce... more The evolution of the light-induced absorption difference spectrum (380-500 nm) of the reaction centers from photosynthetic purple bacteria Rhodobacter sphaeroides has been examined over 200 µ s. The observed changes are interpreted as the effects of proton movement along the H-bond between the primary quinone acceptor and its protein surroundings. A theoretical analysis of the spectral evolution, considering the proton tunneling kinetics, corroborates this interpretation. The electronic state of the primary quinone is stabilized within tens of microseconds; the process is retarded upon deuteration of the reaction center as well as in 90% glycerol, and accelerated upon nondestructive heating to 40 ° C.
The effect of molecular oxygen on the temporary stabilization of an electron at the secondary qui... more The effect of molecular oxygen on the temporary stabilization of an electron at the secondary quinone acceptor (Q B ) of photosynthetic reaction centers (RC) of the purple bacterium Rhodobacter sphaeroides was studied in the preceding work [1]. In the absence of exogenous donors of an electron, photoactivation of pigment-pro tein complexes of RC isolated from chromatophore membranes of Rb. sphaeroides induces fast (characteristic time, ~200 psec) transfer of an electron from the pho toactive bacteriochlorophyll dimer (P) to the primary quinone acceptor (Q A ). Then, within about 200 µsec the electron is transferred to Q B . In the RC of Rb. sphaeroides, the two quinone acceptors are molecules of ubiquinone 10. In further dark reactions the electron returns back to oxidized P. Electrostatic stabilization of the electron in quinone acceptors of RC is due to proton displacement in the RC microenvironment. Changes in the charge state of quinone modify the pK value of the protonated amino acid residues of the RC protein located within the vicinity of 15 17 Å [2 4].
Uploads
Papers by Noks Petr