The proton to electron stoichiometry of steady-state photosynthesis in living plants: A proton-pumping Q cycle is continuously engaged

被引:150
作者
Sacksteder, CA [1 ]
Kanazawa, A [1 ]
Jacoby, ME [1 ]
Kramer, DM [1 ]
机构
[1] Washington State Univ, Inst Biol Chem, Pullman, WA 99164 USA
关键词
steady-state electron and proton transfer; chemiosmotic coupling; cyclic electron transfer; energy budget;
D O I
10.1073/pnas.97.26.14283
中图分类号
O [数理科学和化学]; P [天文学、地球科学]; Q [生物科学]; N [自然科学总论];
学科分类号
07 ; 0710 ; 09 ;
摘要
A noninvasive technique is introduced with which relative proton to electron stoichiometries (H+/e(-) ratios) for photosynthetic electron transfer can be obtained from leaves of living plants under steady-state illumination, Both electron and proton transfer fluxes were estimated by a modification of our previously reported dark-interval relaxation kinetics (DIRK) analysis, in which processes that occur upon rapid shuttering of the actinic light are analyzed. Rates of turnover of linear electron transfer through the cytochrome (cyt) b(6)f complex were estimated by measuring the DIRK signals associated with reduction of cyt f and P-700 The rates of proton pumping through the electron transfer chain and the CF0-CF1 ATP synthase (ATPase) were estimated by measuring the DIRK signals associated with the electrochromic shifting of pigments in the light-harvesting complexes, Electron transfer fluxes were also estimated by analysis of saturation pulse-induced changes in chlorophyll a fluorescence yield. It was shown that the H+/e(-) ratio, with respect to both cyt b(6)f complex and photosystem (PS) II turnover, was constant under low to saturating illumination in intact tobacco leaves. Because a H+/e(-) ratio of 3 at a low light is generally accepted, we infer that this ratio is maintained under conditions of normal (unstressed) photosynthesis, implying a continuously engaged, proton-pumping Q cycle at the cyt b(6)f complex.
引用
收藏
页码:14283 / 14288
页数:6
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