Gerencsér László, Maróti Péter
Department of Biophysics, University of Szeged, Egyetem utca 2, Szeged, 6722, Hungary.
Eur Biophys J. 2008 Sep;37(7):1195-205. doi: 10.1007/s00249-008-0290-3. Epub 2008 Mar 27.
The steady-state operation of photosynthetic reaction center from Rhodobacter sphaeroides was investigated by measuring the rate of cytochrome photo-oxidation under intensive continuous illumination (808 nm, 5 W cm(-2)). The native quinone UQ10 in Q(B) binding site of the reaction center was substituted by tailless UQ0 and the binding parameters and the turnover rate of the UQ0 was studied to test the recently discovered light-intensity dependent acceptor side effect (Gerencsér and Maróti 2006). The binding parameters of UQ0 (k(on) = 2.1 x 10(5) M(-1) s(-1) and k(off) = 100 s(-1)) were characteristic to the RC exposed to high light-intensity. The dissociation constant (K (D) = 480 microM) determined under high light intensity is 2-3 times larger than that determined from flash-experiments. The light-intensity dependent acceleration of cytochrome turnover measured on reaction center of inhibited proton binding was independent of the type of the quinone and was sensitive only to the size ("pressure") of the quinone pool. The dissociation constants of different types of semiquinones show similarly high (several orders of magnitude) increase in the modified conformation of the Q(B) binding pocket due to high intensity of illumination. This result indicates the exclusive role of the quinone headgroup in the binding of semiquinone to different conformations of the protein.
通过在强连续光照（808纳米，5瓦/平方厘米）下测量细胞色素光氧化速率，研究了球形红细菌光合反应中心的稳态运行。反应中心Q(B)结合位点的天然醌UQ10被无尾UQ0取代，并研究了UQ0的结合参数和周转速率，以测试最近发现的光强依赖性受体侧效应（Gerencsér和Maróti，2006年）。UQ0的结合参数（k(on)=2.1×10(5) M(-1) s(-1)和k(off)=100 s(-1)）是暴露于高光强下的反应中心的特征。在高光强下测定的解离常数（K(D)=480微摩尔）比从闪光实验中测定的解离常数大2至3倍。在抑制质子结合的反应中心上测得的细胞色素周转的光强依赖性加速与醌的类型无关，仅对醌池的大小（“压力”）敏感。由于光照强度高，不同类型半醌的解离常数在Q(B)结合口袋的修饰构象中同样显示出高（几个数量级）的增加。这一结果表明醌头基在半醌与蛋白质不同构象结合中的独特作用。
