Visser J W, Rijgersberg C P, Gast P
Biochim Biophys Acta. 1977 Apr 11;460(1):36-46. doi: 10.1016/0005-2728(77)90149-9.
Electron paramagnetic resonance (EPR) and optical absorbance difference spectra and kinetics upon illumination by saturating flashes and continuous light of spinach chloroplasts frozen under various conditions were measured between 10 and 180 K. 1. At 100 K illumination with continuous light caused an EPR signal which decayed during the light in about 30 ms. This change is probably due to the reduction of P+-680, the oxidized primary electron donor of Photosystem II, by a secondary electron donor, cytochrome b-559. Flash illumination yielded the previously observed rapid (2 ms) transient. This transient has been ascribed to a back-reaction of the two primary reagents of Photosystem II (Malkin, R. and Bearden, A.J. (1975) Biochim. Biophys. Acta 396, 250-259; Visser, J.W.M. (1975) Thesis, Leiden). 2. Between 10 and 40 K, illumination with continuous light showed a transient which decayed in about 500 ms. The extent decreased with increasing temperature. However, the half time appeared to be temperature independent. This signal was also attributed to P+-680. 3. At 180 K it appeared to be impossible to observe the 2 and 30 ms components in dark frozen chloroplasts. However, they could be observed again if two short saturating flashes were given shortly before freezing. These changes seem to be dependent on the S-state of the reaction center. 4. After oxidizing the sample with ferricyanide (Eh = 540 mV), the light induced absorbance difference spectrum showed a bleaching near 676 nm. This change is ascribed to the irreversible oxidation of a dimeric chlorophyll molecule which acts as electron donor to P+-680 under these conditions. 5. Titration curves of the irreversible light-induced absorbance change at 676 nm and the irreversible light-induced EPR change near g = 2.00 provide strong evidence that these two changes reflect the same compound. Finally, a model is given to explain the observed reactions of Photosystem II at 10-180 K. The model involves three different ultimate and one intermediate electron donor to P+-680 at these temperatures.
在10至180K之间，测量了在各种条件下冷冻的菠菜叶绿体经饱和闪光和连续光照后，其电子顺磁共振（EPR）、光吸收差光谱及动力学。1. 在100K时，连续光照产生一个EPR信号，该信号在光照期间约30毫秒内衰减。这种变化可能是由于光系统II的氧化初级电子供体P+-680被二级电子供体细胞色素b-559还原所致。闪光照射产生了先前观察到的快速（2毫秒）瞬变。这种瞬变归因于光系统II的两种初级试剂的反向反应（马尔金，R.和比尔登，A.J.（1975年）《生物化学与生物物理学报》396，250 - 259；维瑟，J.W.M.（1975年）论文，莱顿）。2. 在10至40K之间，连续光照显示出一个在约500毫秒内衰减的瞬变。其程度随温度升高而降低。然而，半衰期似乎与温度无关。该信号也归因于P+-680。3. 在180K时，似乎不可能在黑暗冷冻的叶绿体中观察到2毫秒和30毫秒的成分。然而，如果在冷冻前不久给予两个短的饱和闪光，它们又可以被观察到。这些变化似乎取决于反应中心的S态。4. 用铁氰化物（Eh = 540 mV）氧化样品后，光诱导吸收差光谱在676纳米附近出现漂白。这种变化归因于二聚叶绿素分子的不可逆氧化，在这些条件下该分子作为P+-680的电子供体。5. 676纳米处不可逆光诱导吸收变化和g = 2.00附近不可逆光诱导EPR变化的滴定曲线提供了有力证据，表明这两种变化反映的是同一化合物。最后，给出了一个模型来解释在10 - 180K时光系统II的观察到的反应。该模型涉及在这些温度下P+-680的三种不同的最终电子供体和一种中间电子供体。
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