Shinkarev V P, Wraight C A
Department of Plant Biology, University of Illinois, Urbana, IL 61801, USA.
Proc Natl Acad Sci U S A. 1993 Mar 1;90(5):1834-8. doi: 10.1073/pnas.90.5.1834.
Flash-induced oxygen evolution in the thylakoids of plants and algae exhibits damped oscillations with period four. These are well described by the S-state model of Kok et al. [Kok, B., Forbush, B. & McGloin, M. (1970) Photochem. Photobiol. 11, 457-475], with damping provided by empirical misses and double hits in the reaction center of photosystem II. Here we apply a mechanistic interpretation of misses as mainly determined by reaction centers that are inactive at the time of the flash due to the presence of either P+ or QA, according to the electron transfer equilibria on the donor and acceptor sides of the reaction center. Calculation of misses on this basis, using known or estimated values of the equilibrium constants for electron transfer between the S states and tyrosine Yz, between Yz and P680, as well as between the acceptor plastoquinones, allows a natural description of the flash number dependence of oxygen evolution. The calculated misses are different for each flash-induced reaction center transition. Identification of this mechanism underlying the miss factor for each transition leads to the recognition of two different reaction sequence cycles of photosystem II, with different transition probabilities, producing an intrinsic heterogeneity of photosystem II activity.
植物和藻类类囊体中闪光诱导的氧气释放呈现出周期为四的阻尼振荡。Kok等人的S态模型[Kok, B., Forbush, B. & McGloin, M. (1970) Photochem. Photobiol. 11, 457 - 475]对这些现象有很好的描述，其中阻尼是由光系统II反应中心的经验性未命中和双击中提供的。在这里，我们根据反应中心供体侧和受体侧的电子转移平衡，对未命中进行了一种机理解释，即主要由闪光时由于存在P+或QA而处于非活性状态的反应中心决定。基于此，利用S态与酪氨酸Yz、Yz与P680以及受体质体醌之间电子转移平衡常数的已知或估计值来计算未命中，能够自然地描述氧气释放对闪光次数的依赖性。对于每个闪光诱导的反应中心转变，计算出的未命中情况是不同的。识别每个转变的未命中因子背后的这种机制，导致认识到光系统II的两个不同反应序列循环，具有不同的转变概率，从而产生了光系统II活性的内在异质性。
