Sweetman L L, el-Sayed M A
Department of Chemistry and Biochemistry, University of California, Los Angeles 90024.
FEBS Lett. 1991 May 6;282(2):436-40. doi: 10.1016/0014-5793(91)80531-7.
A Scatchard plot for the strongly bound Eu3+ to deionized bacteriorhodopsin (bR) was made using a method based on measuring the concentration of unbound Eu3+ from its fluorescence intensity. The results suggest that the first mole of Eu3+ added to a mole of bR is strongly bound by displacing 2-3 protons. In order to reconcile this result with the previous time-resolved fluorescence studies on Eu(3+)-regenerated bR, which showed the presence of 3 sites of comparable binding constants, one is forced to conclude that the emission from the strongly bound Eu3+ is completely quenched, e.g. by energy transfer to the retinal. For this to take place, the Eu3+ must be within a few A from the retinal, i.e. within the retinal pocket (the active site). The possible importance of this conclusion to the deprotonation mechanism of the protonated Schiff base, the switch of the proton pump in bR, is discussed.
使用一种基于通过荧光强度测量未结合的Eu3+浓度的方法，绘制了强结合的Eu3+与去离子化细菌视紫红质（bR）的Scatchard图。结果表明，添加到一摩尔bR中的第一摩尔Eu3+通过置换2 - 3个质子而被强烈结合。为了使该结果与先前关于Eu(3+)再生bR的时间分辨荧光研究结果相协调，该研究表明存在3个具有可比结合常数的位点，人们不得不推断强结合的Eu3+的发射被完全淬灭，例如通过能量转移到视黄醛。为了发生这种情况，Eu3+必须在距视黄醛几埃的范围内，即在视黄醛口袋（活性位点）内。讨论了这一结论对质子化席夫碱去质子化机制（bR中质子泵的开关）可能具有的重要性。
