title: Temperature dependence of charge recombination in Heliobacillus mobilis.
abstract: Transient absorption difference spectroscopy was used to study the temperature dependence of the P798+ decay kinetics in heliobacteria. For membrane samples, two components were obtained from the fitting of kinetic traces in the temperature range of 4-29 degrees C. A 3-9 ms component representing the cytochrome (cyt) c oxidation has an activation energy of 33.0 +/- 2.8 kJ/mol. A 12-22 ms component representing either P798+FX- or P798+FA/B- recombination has an activation energy of 15.3 +/- 2.4 kJ/mol. In isolated reaction centers (RC), only one 14 ms component due to P798+FX- recombination was obtained in this temperature range. The Arrhenius plot shows that the recombination rate of this P798+FX- state is temperature independent in the near room temperature range. For RC in the temperature range of 60-298 K, a 12-15 ms decay was obtained at temperatures greater than 240 K. Biphasic decay traces (12-15 ms and 2-4 ms components) were obtained at temperatures between 170 K and 230 K. Only one 2-4 ms component was found at temperatures lower than 160 K. The gradual switchover from the 12-15 ms to the 2-4 ms component upon cooling may indicate the shift of the P798+FX- recombination state to a state that is prior to P798+FX-, although other interpretations can not be excluded. The absorption difference spectrum (delta A @ 160 K - delta A @ 240 K) in the blue region shows a positive amplitude below 405 nm and a negative amplitude above 405 nm implying that the 2-4 ms decay component may be due to the recombination of P798+A1-, where A1 is a quinone-type acceptor.
authors.affiliation: Department of Chemistry and Biochemistry, Arizona State University, Tempe, USA.
authors.forename: H C
authors.initials: HC
authors.lastname: Chiou
authors.forename: R E
authors.initials: RE
authors.lastname: Blankenship
mesh_terms: D001419:Bacteria / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects; D004563:Electrochemistry; D004579:Electron Transport; D004735:Energy Transfer; D007700:Kinetics; D008027:Light; D010777:Photochemistry; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects; D013053:Spectrophotometry; D013696:Temperature
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins