A one-site, two-state model for the binding of anions in photosystem II
A one-site, two-state model for the binding of anions in photosystem II
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DOI：
10.1021/bi961244s
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发表时间：
1996-11-12
期刊：
影响因子：
2.9
通讯作者：
Andreasson, LE
中科院分区：
文献类型：
--
作者：
Lindberg, K;Andreasson, LE
光系统 II 膜在无 Cl- 缓冲液中透析以去除结合的 Cl-，损失了约 65% 的对照活性。对无 Cl 膜的光强度研究表明，在无 Cl 介质中测量时，所有 PS II 中心都能以对照速率的 35% 左右放出氧气。通过添加相当高浓度的 Cl- (K-d = 0.5 mM)，Cl- 耗尽的膜立即（< 15 s）重新激活至原始活性的 85-90%，但是当重新激活后立即在无 Cl- 培养基中稀释膜时，Cl- 和活性立即丧失。然而，Cl- 结合的稳定可以通过在 Cl- 存在下延长孵育来实现。几分钟内就发生了向稳定结合的转变，随后使用 Cl-36(-)。稳定结合的进一步特征是 K-d 为 20 μM，解离时间为 1/2 [Lindberg et al. 2014]。 （1993）光合作用。资源。 38、401-408]。使用 EPR 研究了 Cl- 去除对 S-2 信号的影响。 Cl- 的消耗伴随着强度向 g = 4.1 信号的转变，但牺牲了多线信号。当 Cl- 或 Br- 但不是 F- 添加到耗尽的 PS II 膜时，信号的原始分布立即恢复（< 30 s）。我们认为，负责高氧释放活性和 S-2 态正常 EPR 特性的 Cl--结合可能以高亲和力（K-d = 20 μM）和缓慢交换（t(1/2) = 1 h）或低亲和力（K-d = 0.5）的形式发生。 mM) 和快速交换 (t(1/2) < 15 s)。我们的结果表明 Br- 而不是 F- 具有与 Cl- 类似的结合模式。高亲和力状态是正常的结合状态，但是一旦Cl-被去除，它将首先以低亲和力、快速交换的方式重新结合，然后转变为高亲和力、缓慢交换的结合模式。
Photosystem II membranes, dialyzed against a Cl--free buffer to remove bound Cl-, lost about 65% of the control activity. A light-intensity study of the Cl--free membranes showed that all PS II centers were able tn evolve oxygen at about 35% of the control rate when measured in Cl--free medium. The Cl--depleted membranes were immediately (< 15 s) reactivated to 85-90% of the original activity by the addition of fairly high concentrations of Cl- (K-d = 0.5 mM), but both Cl- and the activity were promptly lost when the membranes immediately after reactivation were diluted in a Cl--free medium. However, stabilization of Cl--binding could be accomplished by prolonged incubation in the presence of Cl-. The transition to stable binding, followed using Cl-36(-), occurred over several minutes. The stable binding was further characterized by a K-d Of 20 mu M and a t(1/2) for dissociation of about 1 h [Lindberg et al. (1993) Photosynth. Res. 38, 401-408]. The effects on S-2 signals of removal of Cl- were studied using EPR. The depletion of Cl- was accompanied by a shift in intensity toward the g = 4.1 signal at the expense of the multiline signal. When Cl- or Br- but not F- was added to the depleted PS II membranes, the original distribution of the signals was immediately (< 30 s) restored, We propose that Cl--binding responsible for high oxygen-evolution activity and normal EPR properties of the S-2 State may occur either as high affinity (K-d = 20 mu M) and slowly exchanging (t(1/2) = 1 h), or as low affinity (K-d = 0.5 mM) and rapidly exchanging (t(1/2) < 15 s). Our results suggest that Br- but not F- has a mode of binding similar to that of Cl-. The high-affinity state is the normal state of binding, but once Cl- has been removed, it will first rebind as low-affinity, rapidly exchanging followed by conversion into a high-affinity, slowly exchanging mode of binding.