Kono M, Misra S, Ebrey T G
Biophysics Program, University of Illinois, Urbana 61801.
FEBS Lett. 1993 Sep 27;331(1-2):31-4. doi: 10.1016/0014-5793(93)80291-2.
We have measured the current generated by light-activated proton release from bacteriorhodopsin into solution as a function of both pH and ionic strength. We find that proton release into solution decreases with increasing pH with an intrinsic pKa of 8.2 +/- 0.2. This pH dependence indicates that the deprotonation of a certain group inhibits or abolishes proton release. Under physiological conditions, this group either releases a proton directly into solution or interacts with the site of proton release. The most immediate candidates for this protonatable species are tyrosine-57, tyrosine-185, arginine-82, and water; acting individually or cooperatively. The salt dependence of the apparent pKa of this group also allows us to calculate the surface charge density of about -5 charges per bacteriorhodopsin, compatible with previous estimates.
我们测量了光激活视紫红质向溶液中释放质子所产生的电流，该电流是pH值和离子强度的函数。我们发现，随着pH值升高，向溶液中释放的质子减少，其固有pKa为8.2±0.2。这种对pH值的依赖性表明，某一基团的去质子化会抑制或消除质子释放。在生理条件下，该基团要么直接向溶液中释放质子，要么与质子释放位点相互作用。这种可质子化物种最直接的候选者是酪氨酸-57、酪氨酸-185、精氨酸-82和水；它们单独或协同起作用。该基团表观pKa的盐依赖性还使我们能够计算出每个视紫红质表面电荷密度约为-5个电荷，这与之前的估计相符。
