Identification of the proton pathway in bacterial reaction centers: inhibition of proton transfer by binding of Zn2+ or Cd2+.
Identification of the proton pathway in bacterial reaction centers: inhibition of proton transfer by binding of Zn2+ or Cd2+.
复制标题
细菌反应中心质子途径的鉴定：通过结合 Zn2 或 Cd2 抑制质子转移。
DOI：
10.1073/pnas.96.11.6183
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发表时间：
1999
影响因子：
11.1
通讯作者：
Okamura,MY
中科院分区：
文献类型：
--
作者：
Paddock,ML;Graige,MS;Feher,G;Okamura,MY
球形杆菌的反应中心（RC）通过光诱导结合的醌分子QB（二级醌受体）的双电子、双质子还原，将光转化为化学能。到目前为止，质子转移到qsite的独特途径尚未确定。为了研究质子转移的分子基础，我们研究了外源金属离子结合对质子辅助电子转移动力学的影响kab (2)（QA−•QB−••+ H+→QA(QBH)−，其中qa1为一级醌受体）。Zn2+和Cd2+与RC （KD≤0.5 μM）发生化学计量结合，kab(2)的观测值分别降低了10倍和20倍（pH 8.0）。结合的金属改变了kab(2)反应的机理。在原生RCs中，基于kAB(2)对电子转移驱动力的依赖，kAB(2)先前被证明受电子转移的速率限制。在加入Zn2+或Cd2+后，kAB(2)几乎与电子驱动力无关，这意味着质子转移速率降低（≥102倍），成为限速步骤。金属结合对电荷重组反应D+•QAQB−•→dqaqb没有影响，说明结合位点距离QB较远（bbb10 Å）。初步的x射线结构分析证实了这一假设。由金属离子的化学计量结合引起的质子转移速率的巨大变化表明，质子进入RC有一个主要的位置，质子从这个位置转移到QB−•。
The reaction center (RC) fromRhodobacter sphaeroidesconverts light into chemical energy through the light induced two-electron, two-proton reduction of a bound quinone molecule QB(the secondary quinone acceptor). A unique pathway for proton transfer to the QBsite had so far not been determined. To study the molecular basis for proton transfer, we investigated the effects of exogenous metal ion binding on the kinetics of the proton-assisted electron transferkAB(2)(QA−•QB−•+ H+→ QA(QBH)−, where QAis the primary quinone acceptor). Zn2+and Cd2+bound stoichiometrically to the RC (KD≤ 0.5 μM) and reduced the observed value ofkAB(2)10-fold and 20-fold (pH 8.0), respectively. The bound metal changed the mechanism of thekAB(2)reaction. In native RCs,kAB(2)was previously shown to be rate-limited by electron transfer based on the dependence ofkAB(2)on the driving force for electron transfer. Upon addition of Zn2+or Cd2+,kAB(2)became approximately independent of the electron driving force, implying that the rate of proton transfer was reduced (≥ 102-fold) and has become the rate-limiting step. The lack of an effect of the metal binding on the charge recombination reaction D+•QAQB−•→ DQAQBsuggests that the binding site is located far (>10 Å) from QB. This hypothesis is confirmed by preliminary x-ray structure analysis. The large change in the rate of proton transfer caused by the stoichiometric binding of the metal ion shows that there is one dominant site of proton entry into the RC from which proton transfer to QB−•occurs.