文章基本信息

标题：Identification of the proton pathway in bacterial reaction centers: Both protons associated with reduction of QB to QBH2 share a common entry point
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作者：Pia Ädelroth ; Mark L. Paddock ; Laura B. Sagle 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2000
卷号：97
期号：24
页码：13086-13091
DOI：10.1073/pnas.230439597
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The reaction center from Rhodobacter sphaeroides uses light energy for the reduction and protonation of a quinone molecule, QB. This process involves the transfer of two protons from the aqueous solution to the protein-bound QB molecule. The second proton, H+(2), is supplied to QB by Glu-L212, an internal residue protonated in response to formation of QA- and QB-. In this work, the pathway for H+(2) to Glu-L212 was studied by measuring the effects of divalent metal ion binding on the protonation of Glu-L212, which was assayed by two types of processes. One was proton uptake from solution after the one-electron reduction of QA (DQA[->]D+QA-) and QB (DQB[->]D+QB-), studied by using pH-sensitive dyes. The other was the electron transfer kAB(1) (QA-QB[->]QAQB-). At pH 8.5, binding of Zn2+, Cd2+, or Ni2+ reduced the rates of proton uptake upon QA- and QB- formation as well as kAB(1) by {approx}an order of magnitude, resulting in similar final values, indicating that there is a common rate-limiting step. Because D+QA- is formed 105-fold faster than the induced proton uptake, the observed rate decrease must be caused by an inhibition of the proton transfer. The Glu-L212[->]Gln mutant reaction centers displayed greatly reduced amplitudes of proton uptake and exhibited no changes in rates of proton uptake or electron transfer upon Zn2+ binding. Therefore, metal binding specifically decreased the rate of proton transfer to Glu-L212, because the observed rates were decreased only when proton uptake by Glu-L212 was required. The entry point for the second proton H+(2) was thus identified to be the same as for the first proton H+(1), close to the metal binding region Asp-H124, His-H126, and His-H128.
关键词：Rhodobacter sphaeroides ; proton transfer ; electron transfer ; protein dynamics