Rova E M, Mc Ewen B, Fredriksson P O, Styring S
Department of Biochemistry, Chemical Center, Lund University, Box 124, S-221 00 Lund, Sweden.
J Biol Chem. 1996 Nov 15;271(46):28918-24. doi: 10.1074/jbc.271.46.28918.
The process of photoactivation has been studied in dark grown cells of Chlamydomonas reinhardtii. A mutant, FUD 39, lacking the Cl--concentrating 23-kDa psbP protein of photosystem II was found to have a decreased capability to perform photoactivation. The yield of the process never reached wild type level, and contrary to the wild type, it was highly dependent on the intensity of the activating light, with a very narrow optimum around 1 microE m-2 s-1. The different behavior in the mutant can be explained by a requirement for a longer dark period, between the two photoacts, during the photoactivation. This is proposed to reflect the decreased Cl- affinity in the mutant. Photoactivation in the mutant was also found to be very sensitive to competing photoinhibitory processes. The inhibition was located to the donor side of photosystem II and affected the photoactivation capability before electron transfer from Tyrz was inhibited. We propose an extended model for photoactivation in which an intermediate that is sensitive to photoinhibition is formed if Cl- is not functionally bound to the manganese cluster.
人们已经在莱茵衣藻的黑暗生长细胞中研究了光激活过程。发现一个缺失光系统II中23 kDa的Cl⁻浓缩psbP蛋白的突变体FUD 39进行光激活的能力有所下降。该过程的产量从未达到野生型水平，并且与野生型相反，它高度依赖于激活光的强度，在1微爱因斯坦·米⁻²·秒⁻¹左右有一个非常窄的最佳值。突变体中不同的行为可以通过光激活过程中两次光作用之间需要更长的黑暗期来解释。这被认为反映了突变体中Cl⁻亲和力的降低。还发现突变体中的光激活对竞争性光抑制过程非常敏感。抑制作用位于光系统II的供体侧，并且在从Tyrz进行电子转移被抑制之前就影响了光激活能力。我们提出了一个扩展的光激活模型，其中如果Cl⁻没有功能性地结合到锰簇上，就会形成一个对光抑制敏感的中间体。
