Kolodner P, Lukashev E P, Ching Y C, Rousseau D L
Bell Laboratories, Lucent Technologies Inc., Murray Hill, NJ 07974-0636, USA.
Proc Natl Acad Sci U S A. 1996 Oct 15;93(21):11618-21. doi: 10.1073/pnas.93.21.11618.
The application of an external electric field to dry films of Asp-85-->Asn mutant bacteriorhodopsin causes deprotonation of the Schiff base, resulting in a shift of the optical absorption maximum from 600 nm to 400 nm. This is in marked contrast to the case of wild-type bacteriorhodopsin films, in which electric fields produce a red-shifted product whose optical properties are similar to those of the acid-blue form of the protein. This difference is due to the much weaker binding of the Schiff-base proton in the mutant protein, as indicated by its low pK of approximately 9, as compared with the value pK approximately 13 in the wild type. Other bacteriorhodopsins with lowered Schiff-base pK values should also exhibit a field-induced shift in the protonation equilibrium of the Schiff base. We propose mechanisms to account for these observations.
对天冬氨酸85位突变为天冬酰胺的嗜盐菌视紫红质干膜施加外部电场会导致席夫碱去质子化，从而使最大光吸收峰从600纳米移至400纳米。这与野生型嗜盐菌视紫红质膜的情况形成显著对比，在野生型膜中，电场会产生一种红移产物，其光学性质与该蛋白质的酸蓝形式相似。这种差异是由于突变蛋白中席夫碱质子的结合力弱得多，这表现为其约9的低pK值，而野生型的pK值约为13。其他席夫碱pK值降低的嗜盐菌视紫红质也应在席夫碱的质子化平衡中表现出场致位移。我们提出了解释这些观察结果的机制。
