Conformation-activated protonation in reaction centers of the photosynthetic bacterium Rhodobacter sphaeroides.

Kinetics and stoichiometry of proton binding/unbinding induced by intense (1 W cm-2) and continuous illumination were measured in the isolated reaction center (RC) protein from photosynthetic purple bacterium Rhodobacter sphaeroides in the absence of an external electron donor. At high ionic strength (100 mM), large proton release (approximately 6 H+ per RC) was observed at pH 6 and substoichiometric H+-ion binding (approximately 0.3 H+ per RC) at pH 8.

Stabilization of reduced primary quinone by proton uptake in reaction centers of Rhodobacter sphaeroides.

Proton binding stoichiometry and kinetics of charge recombination were measured after single flash excitation in reaction centers from the purple photosynthetic bacterium, Rhodobacter sphaeroides strain R-26, where the native ubiquinone in the primary quinone acceptor site QA was removed and replaced by (benzo-, naphtho-, and anthra-) quinones of various structures and redox midpoint potentials. The observed proton binding stoichiometry was small (0.2-0.

Flash-induced proton transfer in photosynthetic bacteria.

A proton electrochemical potential across the membranes of photosynthetic purple bacteria is established by a light-driven proton pump mechanism: the absorbed light in the reaction center initiates electron transfer which is coupled to the vectorial displacement of protons from the cytoplasm to the periplasm. The stoichiometry and kinetics of proton binding and release can be tracked directly by electric (glass electrodes), spectrophotometric (pH indicator dyes) and conductimetric techniques. The primary step in the formation of the transmembrane chemiosmotic potential is the uptake of two protons by the doubly reduced secondary quinone in the reaction center and the subsequent exchange of hydroquinol for quinone from the membrane quinone-pool.

Comparative antioxidant enzyme study in freshwater fishes. II. Distribution of antioxidant enzymes and lipid peroxidation in omnivorous fish organs.

Comparative studies were performed on the activities of superoxide dismutases, catalase and glutathione peroxidase in organ homogenates from three omnivorous fishes, the barbel, crucian carp and common carp. The lipid peroxidation and protein contents of organ homogenates were also compared. These comparative measurements primarily provide control values for subsequent toxicological examinations.