Kaminskaya Olga, Shuvalov Vladimir A, Renger Gernot
Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino, Moscow Region 142290, Russia.
Biochemistry. 2007 Jan 30;46(4):1091-105. doi: 10.1021/bi0613022.
The present study provides a thorough analysis of effects on the redox properties of cytochrome (Cyt) b559 induced by two photosystem II (PS II) herbicides [3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and 2,4-dinitro-6-sec-butylphenol (dinoseb)], an acceleration of the deactivation reactions of system Y (ADRY) agent carbonylcyanide-m-chlorophenylhydrazone (CCCP), and the lipophilic PS II electron-donor tetraphenylboron (TPB) in PS II membrane fragments from higher plants. The obtained results revealed that (1) all four compounds selectively affected the midpoint potential (E(m)) of the high potential (HP) form of Cyt b559 without any measurable changes of the E(m) values of the intermediate potential (IP) and low potential (LP) forms; (2) the control values from +390 to +400 mV for HP Cyt b559 gradually decreased with increasing concentrations of DCMU, dinoseb, CCCP, and TPB; (3) in the presence of high TPB concentrations, a saturation of the E(m) decrease was obtained at a level of about +240 mV, whereas no saturation was observed for the other compounds at the highest concentrations used in this study; (4) the effect of the phenolic herbicide dinoseb on the E(m) is independent of the occupancy of the Q(B)-binding site by DCMU; (5) at high concentrations of TPB or dinoseb, an additional slow and irreversible transformation of HP Cyt b559 into IP Cyt b559 or a mixture of the IP and LP Cyt b559 is observed; and (6) the compounds stimulate autoxidation of HP Cyt b559 under aerobic conditions. These findings lead to the conclusion that a binding site Q(C) exists for the studied substances that is close to Cyt b559 and different from the Q(B) site. On the basis of the results of the present study and former experiments on the effect of PQ extraction and reconstitution on HP Cyt b559 [Cox, R. P., and Bendall, D. S. (1974) The functions of plastoquinone and beta-carotene in photosystem II of chloroplasts, Biochim. Biophys. Acta 347, 49-59], it is postulated that the binding of a plastoquinone (PQ) molecule to Q(C) is crucial for establishing the HP form of Cyt b559. On the other hand, the binding of plastoquinol (PQH2) to Q(C) is assumed to cause a marked decrease of E(m), thus, giving rise to a PQH2 oxidase function of Cyt b559. The possible physiological role of the Q(C) site as a regulator of the reactivity of Cyt b559 is discussed.
本研究全面分析了两种光系统II（PS II）除草剂[3-(3,4-二氯苯基)-1,1-二甲基脲（敌草隆）和2,4-二硝基-6-仲丁基苯酚（地乐酚）]、系统Y失活反应加速剂（ADRY）羰基氰-m-氯苯腙（CCCP）以及亲脂性PS II电子供体四苯基硼（TPB）对高等植物PS II膜片段中细胞色素（Cyt）b559氧化还原特性的影响。所得结果表明：（1）所有这四种化合物均选择性地影响Cyt b559高电位（HP）形式的中点电位（E(m)），而中间电位（IP）和低电位（LP）形式的E(m)值无任何可测量的变化；（2）HP Cyt b559的对照值在+390至+400 mV之间，随着敌草隆、地乐酚、CCCP和TPB浓度的增加而逐渐降低；（3）在高TPB浓度下，E(m)降低出现饱和，饱和水平约为+240 mV，而在本研究中使用的最高浓度下，其他化合物未观察到饱和现象；（4）酚类除草剂地乐酚对E(m)的影响与敌草隆对Q(B)结合位点的占据情况无关；（5）在高浓度的TPB或地乐酚存在下，观察到HP Cyt b559向IP Cyt b559或IP和LP Cyt b559混合物的额外缓慢且不可逆的转变；（6）这些化合物在有氧条件下刺激HP Cyt b559的自氧化。这些发现得出结论，在所研究的物质中存在一个与Cyt b559接近且不同于Q(B)位点的Q(C)结合位点。基于本研究结果以及先前关于质体醌（PQ）提取和重组对HP Cyt b559影响的实验[考克斯，R.P.，和本多尔，D.S.（1974年）叶绿体光系统II中质体醌和β-胡萝卜素的功能，生物化学与生物物理学报347，49 - 59]，推测质体醌（PQ）分子与Q(C)的结合对于建立Cyt b559的HP形式至关重要。另一方面，推测质体氢醌（PQH2）与Q(C)的结合会导致E(m)显著降低，从而赋予Cyt b559 PQH2氧化酶功能。讨论了Q(C)位点作为Cyt b559反应性调节剂的可能生理作用。
