Reversible binding of nitric oxide to tyrosyl radicals in photosystem II. Nitric oxide quenches formation of the S3 EPR signal species in acetate-inhibited photosystem II.
Reversible binding of nitric oxide to tyrosyl radicals in photosystem II. Nitric oxide quenches formation of the S3 EPR signal species in acetate-inhibited photosystem II.
复制标题
一氧化氮与光系统 II 中酪氨酰自由基的可逆结合。
DOI：
10.1021/bi961117w
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发表时间：
1996
期刊：
影响因子：
--
通讯作者：
Brudvig,GW
中科院分区：
文献类型：
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作者：
Szalai,VA;Brudvig,GW
在高于 250 K 的温度下连续照射已耗尽钙或氯化物或用氟化物、乙酸盐或氨处理的光系统 II 样品，会产生以 atg= 2.0 为中心的广泛自由基 EPR 信号。这种 EPR 信号称为 S3 EPR 信号，归因于有机自由基与放氧复合物的 S2 态相互作用，产生物质 S2X+（X+= 有机自由基）。酪氨酸自由基已被提议作为负责 S3 EPR 信号的物种。实验证明一氧化氮与核糖核苷酸还原酶中的酪氨酰自由基可逆结合，一氧化氮已被用于探测醋酸盐处理的光系统 II 中的 S3 EPR 信号。在使用贫锰光系统 II 的实验中，发现一氧化氮可逆地与氧化还原活性酪氨酸 YD• 和 YZ• 结合，形成 EPR 沉默加合物。接下来，在一氧化氮存在的情况下，照射醋酸盐处理的光系统 II 以形成 S3 EPR 信号，以测试 S3 EPR 信号的行为是否与 YZ• 类似。在醋酸盐处理的光系统 II 中产生最大 S3 EPR 信号的条件下，在一氧化氮存在下没有观察到 S3 EPR 信号。去除一氧化氮后，可以诱导 S3 EPR 信号。通过一氧化氮猝灭 S3 EPR 信号产生 S2 状态多线 EPR 信号。其振幅是 200 K 照射下不受抑制的光系统 II 的振幅的 45%；该产率与同等条件下但不含一氧化氮的 S3 EPR 信号的产率相同。这些结果表明，S3 EPR 信号是由于构型 S2YZ• 引起的，其中释氧复合物的 S2 态由于与 YZ• 交换和偶极相互作用而给出了展宽的多线 EPR 信号。一氧化氮与 YZ• 结合形成抗磁性 YZ−NO 物质，使 S2 态与 YZ• 解偶联，产生非相互作用的 S2 态多线 EPR 信号物质。
Continuous illumination at temperatures above 250 K of photosystem II samples which have been depleted of calcium or chloride or treated with fluoride, acetate, or ammonia results in production of a broad radical EPR signal centered atg= 2.0. This EPR signal, called the S3 EPR signal, has been attributed to an organic radical interacting with the S2state of the oxygen-evolving complex to give the species S2X+(X+= organic radical). A tyrosine radical has been proposed as the species responsible for the S3 EPR signal. On the basis of experiments demonstrating that nitric oxide binds reversibly to the tyrosyl radical in ribonucleotide reductase, nitric oxide has been used to probe the S3 EPR signal in acetate-treated photosystem II. In experiments using manganese-depleted photosystem II, nitric oxide was found to bind reversibly to both redox-active tyrosines, YD•and YZ•, to form EPR-silent adducts. Next, acetate-treated photosystem II was illuminated to form the S3 EPR signal in the presence of nitric oxide to test whether the S3 EPR signal behaves like YZ•. Under conditions that produce the maximum yield of the S3 EPR signal in acetate-treated photosystem II, no S3 EPR signal was observed in the presence of nitric oxide. Upon removal of nitric oxide, the S3 EPR signal could be induced. Quenching of the S3 EPR signal by nitric oxide yielded an S2-state multiline EPR signal. Its amplitude was 45% of that found for uninhibited photosystem II illuminated at 200 K; this yield is the same as the yield of the S3 EPR signal under equivalent conditions but without nitric oxide. These results suggest that the S3 EPR signal is due to the configuration S2YZ•in which the S2state of the oxygen-evolving complex gives a broadened multiline EPR signal as a result of exchange and dipolar interactions with YZ•. The binding of nitric oxide to YZ•to form a diamagnetic YZ−NO species uncouples the S2state from YZ•, yielding a noninteracting S2-state multiline EPR signal species.