Resolution of electron and proton transfer events in the electrochromismassociated with quinone reduction in bacterial reaction centers
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- 作者：Tiede ; David M. ; Utschig ; Lisa ; Hanson ; Deborah K. ; Gallo ; Dennis M.
- 关键词：bacterial photosynthesis ; electrochromism ; electron transfer ; proton transfer ; quinone ; reaction center
- 刊名：Photosynthesis Research
- 出版时间：1998
- 出版年：1998
- 期刊代码：20_01668595
- 类别：bus
- 卷：55
- 期：2/3
- 页码：267-273
- 数据来源：sp
摘要
We have measured the electrochromic response of the bacteriopheophytin,BPh, and bacteriochlorophyll, BChl, cofactors during theQ<math>_Amath><math>^-math>Q<math>_Bmath> →Q<math>_Amath>Q<math>_Bmath><math>^-math> electron transfer inchromatophores of Rhodobacter (Rb.) capsulatus and Rb. sphaeroides. Theelectrochromic response rises faster in chromatophores and is more clearlybiexponential than it is in isolated reaction centers. The chromatophorespectra can be interpreted in terms of a clear kinetic separation betweenfast electron transfer and slower non-electron transfer events such asproton transfer or protein relaxation. The electrochromic response toelectron transfer exhibits rise times of about 4 µs (70%) and40 µs (30%) in Rb. capsulatus and 4 µs (60%) and80 µs (40%) in Rb. sphaeroides. The BPh absorption band isshifted to nearly equivalent positions in theQ<math>_Amath><math>^-math> and nascent Q<math>_Bmath><math>^-math>states, indicating that the electrochromic perturbation of BPh absorptionfrom the newly formed Q<math>_Bmath><math>^-math> state is comparable tothat of Q<math>_Amath><math>^-math> . Subsequently, partial attenuationof the Q<math>_Bmath><math>^-math> electrochromism occurs with a timeconstant on the order of 200 µs. This can be attributed to partialcharge compensation by H<math>^+math> (or other counter ion) movement intothe Q<math>_Bmath> pocket. Electron transfer events were found to beslower in detergent isolated RCs than in chromatophores, more nearlymonoexponential, and overlap H<math>^+math> transfer, suggesting that achange in rate-limiting step has occurred upon detergent solubilization.