title: Light-induced proton transport by chloroplasts suspended in fluid media at sub-zero temperatures: kinetics and stoichiometry.
abstract: 1. Chloroplasts suspended in a medium containing ethanediol and water (1 : 1, v/v) at -16 degrees C show light-induced proton uptake and subsequent dark efflux. Proton uptake in continuous light showed biphasic kinetics. 2. A 1 ms flash caused a single turnover of the photochemical centres at -16 degrees C. Under the same conditions 3H+ were taken up from the external medium in the presence of methyl viologen as electron acceptor. 3. The flash-induced proton uptake was exponential and monophasic with t1/2 = 3 s. The flash-induced proton release into the thylakoid interior was biphasic, with half-times of less than 0.1 s and 3 s. The fast phase represented approximately 30% of the total release and may be correlated with the oxidation of water. 4. The half-time of reduction of cytochrome f in the dark following illumination in the presence of 2 mM NH4Cl (2.5 s) is similar to the half-time of the slow phase of proton release, suggesting a correlation between the kinetics of cytochrome f reduction and plastoquinol oxidation.
mesh_terms: D002736:Chloroplasts / Q000201:enzymology / Q000378:metabolism*; D003080:Cold Temperature; D003580:Cytochromes / Q000378:metabolism; D006207:Half-Life; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008027:Light; D010777:Photochemistry; D010944:Plants / Q000378:metabolism* / Q000648:ultrastructure; D011522:Protons
chemical_list: D003580:Cytochromes; D011522:Protons