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首页> 外文期刊>Biochemistry >O-18 isotope exchange measurements reveal that calcium is involved in the binding of one substrate-water molecule to the oxygen-evolving complex in photosystem II
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O-18 isotope exchange measurements reveal that calcium is involved in the binding of one substrate-water molecule to the oxygen-evolving complex in photosystem II

机译：O-18同位素交换测量结果表明，钙涉及一个底物水分子与照射系统II中的氧不变复合物的结合

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Direct evidence is presented to show that calcium is inherently involved in the binding of one of the two substrate-water molecules to the oxygen-evolving complex in photosystem II. Previous rapid (millisecond range) O-18 isotope exchange measurements between added (H2O)-O-18 and the photogenerated O-2 have shown that the two substrate-water molecules bind to separate sites throughout the S-state cycle, as revealed by their kinetically distinct rates of O-18 exchange [Hillier, W., and Wydrzynski, T. (2000) Biochemistry; 39, 4399-4405]. Upon extraction of the functionally bound calcium using a either a low-pH/citrate treatment or a NaCl/A23187/EGTA treatment and subsequent reconstitution of activity with strontium, we show for the first time a specific increase in the slow rate of O-18 exchange by a factor of 3-4. This increase in the slow rate of exchange is consistently observed across the S-1, S-2, and S-3 states. In contrast, the fast phase of O-18 exchange in the S-3 state appears to be affected little upon strontium reconstitution, while the fast phases of exchange in the S-1 and S-2 states remain largely unresolvable, at the detectable limits of the current techniques. The results are discussed in terms of a possible substrate bridging structure between the functional calcium and a catalytic manganese ion that gives rise to the slowly exchanging component. [References: 65]
机译：提出了直接证据表明钙本质上涉及两个底物水分子之一与照射系统II中的氧的复合物的结合。以前的快速（毫秒）O-18同位素交换测量在添加（H2O）-O-18和光生O-2之间表明，两个基底水分子在整个S状态循环中与分离的位点结合，如图所示他们的o-18交易所[Hillier，W.和Wydrzynski，T.（2000）生物化学; 39,4399-4405]。在使用低pH /柠檬酸盐处理或NaCl / A23187 / EGTA治疗和随后用锶的重建和随后的活性重建时，我们展示了第一次对O-18的慢速度的第一次提高交换3-4倍。在S-1，S-2和S-3状态下始终观察到慢速交换速率的增加。相反，S-3状态下的O-18交换的快速相位似乎受到锶重构的影响，而S-1和S-2状态的交换的快速相位在可检测的限度下仍未可解放目前的技术。结果在功能钙和催化锰离子之间的可能底物桥接结构方面讨论，所述催化锰离子产生缓慢交换组分。 [参考：65]

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