Isaacson R A, Lendzian F, Abresch E C, Lubitz W, Feher G
Department of Physics, University of California, San Diego, La Jolla 92093, USA.
Biophys J. 1995 Aug;69(2):311-22. doi: 10.1016/S0006-3495(95)79936-2.
The magnitude and orientation of the electronic g-tensor of the primary electron acceptor quinone radical anion, Q-A, has been determined in single crystals of zinc-substituted reaction centers of Rhodobacter sphaeroides R-26 at 275 K and at 80 K. To obtain high spectral resolution, EPR experiments were performed at 35 GHz and the native ubiquinone-10 (UQ10) in the reaction center was replaced by fully deuterated UQ10. The principal values and the direction cosines of the g-tensor axes with respect to the crystal axes a, b, c were determined. Freezing of the single crystals resulted in only minor changes in magnitude and orientation of the g-tensor. The orientation of Q-A as determined by the g-tensor axes deviates only by a few degrees (< or = 8 degrees) from the orientation of the neutral QA obtained from an average of four different x-ray structures of Rb. sphaeroides reaction centers. This deviation lies within the accuracy of the x-ray structure determinations. The g-tensor values measured in single crystals agree well with those in frozen solutions. Variations in g-values between Q-A, Q-B, and UQ10 radical ion in frozen solutions were observed and attributed to different environments.
在275K和80K温度下，已在球形红杆菌R-26的锌取代反应中心的单晶中确定了初级电子受体醌自由基阴离子Q-A的电子g张量的大小和方向。为了获得高光谱分辨率，在35GHz下进行了电子顺磁共振（EPR）实验，并且反应中心中的天然泛醌-10（UQ10）被完全氘代的UQ10所取代。确定了g张量轴相对于晶体轴a、b、c的主值和方向余弦。单晶的冷冻仅导致g张量的大小和方向发生微小变化。由g张量轴确定的Q-A的方向与从球形红杆菌反应中心的四种不同x射线结构的平均值获得的中性QA的方向仅相差几度（≤8度）。这种偏差在x射线结构测定的精度范围内。在单晶中测量的g张量值与在冷冻溶液中的值非常吻合。观察到冷冻溶液中Q-A、Q-B和UQ10自由基离子之间g值的变化，并将其归因于不同的环境。
