Fabian M, Chamorovskiĭ S K, Zakharova N I, Selivanov V A, Kononenko A A
Mol Biol (Mosk). 1981 Mar-Apr;15(2):439-46.
In experiments with reaction centers (RC) preparations of Rps. sphaeroides, strain 1760-1, pH of the suspension medium was found to change under continuous light excitation. The concentration of hydrogen ions starts to decrease fastly (t1/2 = 2--4 s) after the light is on, whereupon it increases slowly, to a steady-state level, within t1/2 = 5--7 min. During the fast phase 0.3 microM H+/1 microM of RC are absorbed and 7--8 microM H+/1 microM of RC are released under the slow phase. The fast phase is suppressed by ortho-phenantroline (10 mM)--an inhibitor of electron transfer from the primary (Fe-quinone complex) to the secondary (quinone) electron acceptors. Glutaraldehyde which is known to modify a protein structure of the RC inhibits the slow phase. The obtained data suggest that fast light-induced pH changes are due to a H+ uptake by the secondary quinoid anion-radical products; slow pH changes are ascribed to structural changes within the RC complex, which lead to a pK shift and/or changes in the amount of dissociating groups on the protein interfacial surface. The conclusion was supported by an observation of light-induced changes in buffer capacity of an RC suspension and by a light-induced increase in the amount of SH-groups titrated by 5.5-dithio-bis(2 nitro)-benzoic acid. The role of conformational dynamics of photoactive pigment--protein complexes in the functions of the RC is discussed.
在对球形红假单胞菌（Rps. sphaeroides）1760 - 1菌株的反应中心（RC）制剂进行的实验中，发现悬浮介质的pH值在持续光照激发下会发生变化。光照开启后，氢离子浓度开始快速下降（半衰期t1/2 = 2 - 4秒），随后在t1/2 = 5 - 7分钟内缓慢上升至稳态水平。在快速阶段，每微摩尔RC吸收0.3微摩尔H⁺，在缓慢阶段每微摩尔RC释放7 - 8微摩尔H⁺。快速阶段受到邻菲罗啉（10 mM）的抑制，邻菲罗啉是从初级（铁 - 醌复合物）到次级（醌）电子受体的电子转移抑制剂。已知能改变RC蛋白质结构的戊二醛会抑制缓慢阶段。所获得的数据表明，快速的光诱导pH变化是由于次级醌阴离子自由基产物吸收H⁺所致；缓慢的pH变化归因于RC复合物内部的结构变化，这导致pK值移动和/或蛋白质界面表面解离基团数量的变化。通过观察RC悬浮液缓冲容量的光诱导变化以及5,5 - 二硫代双（2 - 硝基）苯甲酸滴定的SH基团数量的光诱导增加，支持了这一结论。文中还讨论了光活性色素 - 蛋白质复合物的构象动力学在RC功能中的作用。
