Debus R J, Barry B A, Sithole I, Babcock G T, McIntosh L
MSU-DOE Plant Research Laboratory, Department of Chemistry, Michigan State University, East Lansing 48824.
Biochemistry. 1988 Dec 27;27(26):9071-4. doi: 10.1021/bi00426a001.
Photosystem II contains two redox-active tyrosines. One of these, YZ, reduces the reaction center chlorophyll, P680, and transfers the oxidizing equivalent to the oxygen-evolving complex. The second, YD, has a long-lived free radical state of unknown function. We recently established that YD is Tyr-160 of the D2 polypeptide by site-directed mutagenesis of a psbD gene in the unicellular cyanobacterium Synechocystis 6803 [Debus, R. J., Barry, B. A., Babcock, G. T., & McIntosh, L. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 427-430]. YZ is most likely the symmetry-related Tyr-161 of the D1 polypeptide. To test this hypothesis, we have changed Tyr-161 to phenylalanine by site-directed mutagenesis of a psbA gene in Synechocystis. The resulting mutant assembles PSII, as judged by its ability to produce the stable Y+D radical, but is unable to grow photosynthetically and exhibits altered fluorescence properties. The nature of the fluorescence change indicates that forward electron transfer to P+680 is disrupted in the mutant. These results provide strong support for our identification of Tyr-161 in the D1 polypeptide with YZ.
光系统II含有两个具有氧化还原活性的酪氨酸。其中一个，YZ，还原反应中心叶绿素P680，并将氧化当量传递给放氧复合体。另一个，YD，具有寿命较长的自由基状态，其功能未知。我们最近通过对单细胞蓝藻集胞藻6803中的psbD基因进行定点诱变，确定YD是D2多肽的Tyr-160 [德布斯，R. J.，巴里，B. A.，巴布科克，G. T.，& 麦金托什，L.（1988年）美国国家科学院院刊85，427 - 430]。YZ很可能是D1多肽中与之对称的Tyr-161。为了验证这一假设，我们通过对集胞藻中的psbA基因进行定点诱变，将Tyr-161替换为苯丙氨酸。根据产生稳定的Y+D自由基的能力判断，所得突变体组装了光系统II，但无法进行光合生长，并表现出荧光特性改变。荧光变化的性质表明，突变体中向P+680的正向电子传递被破坏。这些结果为我们将D1多肽中的Tyr-161鉴定为YZ提供了有力支持。
