Braiman M S, Mogi T, Marti T, Stern L J, Khorana H G, Rothschild K J
Physics Department and Program in Cellular Biophysics, Boston University, Massachusetts 02215.
Biochemistry. 1988 Nov 15;27(23):8516-20. doi: 10.1021/bi00423a002.
Fourier transform infrared (FTIR) difference spectra have been obtained for the bR----K, bR----L, and bR----M photoreactions in bacteriorhodopsin mutants in which Asp residues 85, 96, 115, and 212 have been replaced by Asn and by Glu. Difference peaks that had previously been attributed to Asp COOH groups on the basis of isotopic labeling were absent or shifted in these mutants. In general, each COOH peak was affected strongly by mutation at only one of the four residues. Thus, it was possible to assign each peak tentatively to a particular Asp. From these assignments, a model for the proton-pumping mechanism of bR is derived, which features proton transfers among Asp-85, -96, and -212, the chromophore Schiff base, and other ionizable groups within the protein. The model can explain the observed COOH peaks in the FTIR difference spectra of bR photointermediates and could also account for other recent results on site-directed mutants of bR.
已获得细菌视紫红质突变体中bR→K、bR→L和bR→M光反应的傅里叶变换红外（FTIR）差谱，其中天冬氨酸残基85、96、115和212已被天冬酰胺和谷氨酸取代。在这些突变体中，以前基于同位素标记归因于天冬氨酸COOH基团的差峰不存在或发生了位移。一般来说，每个COOH峰仅受到四个残基中一个残基突变的强烈影响。因此，可以初步将每个峰归属于特定的天冬氨酸。根据这些归属，推导了一个bR质子泵浦机制的模型，其特征是天冬氨酸-85、-96和-212、发色团席夫碱以及蛋白质内其他可电离基团之间的质子转移。该模型可以解释在bR光中间体的FTIR差谱中观察到的COOH峰，也可以解释关于bR定点突变体的其他最新结果。
