Mechanism of methanol inhibition of photosynthetic water oxidation as studied by Fourier transform infrared difference and time-resolved infrared spectroscopies
Mechanism of methanol inhibition of photosynthetic water oxidation as studied by Fourier transform infrared difference and time-resolved infrared spectroscopies
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傅里叶变换红外差值和时间分辨红外光谱研究甲醇抑制光合水氧化的机理
DOI：
10.1021/acs.biochem.8b00596
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发表时间：
2018
期刊：
影响因子：
2.9
通讯作者：
and T. Noguchi
中科院分区：
文献类型：
--
作者：
H. Yata;and T. Noguchi
光合水氧化是在光系统II的Mn 4CaO 5簇中进行的。在这项研究中，我们研究了甲醇，水的模拟物，对水的氧化反应和它的相互作用位点，利用傅里叶变换红外光谱（FTIR）差和时间分辨红外光谱（TRIR）。闪光诱导的FTIR差谱测量表明，甲醇主要降低了S_3 → S_0跃迁的效率。TRIR测量进一步表明，甲醇使S2→ S3和S3→ S 0跃迁的速率减慢。FTIR差谱分析表明，甲醇对Mn 4CaO 5簇合物S1→ S2跃迁的影响主要表现在主链的酰胺I和酰胺II谱带的变化，而羧酸根、组氨酸侧链和簇合物附近的水网络谱带的变化不大.用乙醇和2-丙醇也观察到类似的趋势。用~（18）O标记的甲醇在S_2-S_1谱中进一步确认了甲醇的C-O伸缩振动。这些结果表明，甲醇和小的醇被绑定附近的Mn 4CaO 5集群，但没有直接的相互作用。它们可能取代了Mn 4CaO 5簇周围的水通道中的水分子，可能与主链酰胺相互作用。因此，这表明，这种取代水与甲醇或少量的醇抑制水/质子转移过程中的S2→ S3和S3→ S 0的转变，这反过来又提供了实验支持的观点，这两个转变涉及水的吸收和质子释放过程。
Photosynthetic water oxidation is performed at the Mn4CaO5cluster in photosystem II. In this study, we investigated the effect of methanol, an analogue of water, on the water oxidation reaction and its interaction site using Fourier transform infrared (FTIR) difference and time-resolved infrared (TRIR) spectroscopies. Flash-induced FTIR difference measurement of the S-state cycle showed that methanol decreases mainly the efficiency of the S3→ S0transition. TRIR measurement further showed that methanol slowed the rates of the S2→ S3and S3→ S0transitions. FTIR difference spectra upon the S1→ S2transition exhibited prominent methanol-induced changes in the amide I and II bands of the main chains, whereas little change was observed in the bands of carboxylate groups, histidine side chains, and a water network in the vicinity of the Mn4CaO5cluster. Similar tendencies were also observed with ethanol and 2-propanol. The C–O stretching vibration of methanol was further identified in the S2-minus-S1spectrum using18O-labeled methanol. These results indicate that methanol and small alcohols are bound near the Mn4CaO5cluster but with no direct interaction. They probably replace a water molecule in a water channel around the Mn4CaO5cluster, possibly interacting with a main chain amide. It is thus suggested that this replacement of water with methanol or a small alcohol inhibits water/proton transfer during the S2→ S3and S3→ S0transitions, which in turn provides experimental support for the view that these two transitions involve the water uptake and proton release processes.