Kinetics of light-induced redox changes of high-potential cytochrome in the chromatophores of purple sulfur bacteria Ectothiorhodospira shaposhnikovii

Light-induced redox changes of high-potential cytochrome Ch (Em 7.0 = + 290 mV) have been studied. It was found that after switching off the actinic light there is a delay in the cytochrome dark reduction. The extent of the delay depends on the intensity of actinic light, being the more the higher the intensity. A simple kinetic model is proposed to explain both kinetics of redox changes of the cytochrome and dependence of the delay upon the intensity of actinic light.     

Kinetics of ubisemiquinone redox changes in primary reactions of bacterial photosynthesis

Absorbance changes at 450 nm of the semiquinone form of the secondary electron acceptor were studied in chromatophores of Rhodospirillum rubrum. When chromatophores are illuminated by a series of single turnover flashes ubisemiquinone is formed and destroyed on alternate flashes at ambient redox potential from 100 to 250 mV. A simple kinetic model of the binary oscillations is suggested. On the base of the model it is shown that the rate constant of electron transfer from primary to secondary quinone after the first flash is larger that after the second flash. Cooperativity in electron transfer from primary to secondary quinone can be explained by electrostatic interactions of charged carriers.     

Kinetic model of the operation of a 2-electron switch in the photosynthetic reaction center of bacteria

A mathematical model, describing the binary oscillation of the concentration of semiquinone form of the secondary acceptor (ubiquinone) in photosynthetic reaction center of purple bacteria is proposed. This model takes into account both the changes of the ubiquinone state when the chromatophores are subjected to short flashes of light, and the successive dark relaxation of the semiquinone form. The model allows to calculate such characteristics as the dependence of the flash number, the stationary level of semiquinone form which is being established, when the flash number increases, the velocity which the concentration of semiquinone form is aspirating towards this stationary level and other characteristics. The model shows that the quantum yield of primary charge separation on the reaction center is higher after odd-number flashes then after even-number flashes.