Earnest T N, Herzfeld J, Rothschild K J
Department of Physics, Boston University, Massachusetts 02115.
Biophys J. 1990 Dec;58(6):1539-46. doi: 10.1016/S0006-3495(90)82498-X.
The secondary structure of bacteriorhodopsin has been investigated by polarized Fourier transform infrared spectroscopy combined with hydrogen/deuterium exchange, isotope labeling and resolution enhancement methods. Oriented films of purple membrane were measured at low temperature after exposure to H2O or D2O. Resolution enhancement techniques and isotopic labeling of the Schiff base were used to assign peaks in the amide I region of the spectrum. alpha-helical structure, which exhibits strong infrared dichroism, undergoes little H/D exchange, even after 48 h of D2O exposure. In contrast, non-alpha-helical structure, which exhibits little dichroism, undergoes rapid H/D exchange. A band at 1,640 cm-1, which has previously been assigned to beta-sheet structure, is found to be due in part to the C = N stretching vibration of protonated Schiff base of the retinylidene chromophore. We conclude that the membrane spanning regions of bR consist predominantly of alpha-helical structure whereas most beta-type structure is located in surface regions directly accessible to water.
通过偏振傅里叶变换红外光谱结合氢/氘交换、同位素标记和分辨率增强方法，对细菌视紫红质的二级结构进行了研究。将紫色膜的定向膜在暴露于H₂O或D₂O后于低温下进行测量。使用分辨率增强技术和席夫碱的同位素标记来确定光谱酰胺I区域中的峰。表现出强烈红外二色性的α-螺旋结构，即使在暴露于D₂O 48小时后，H/D交换也很少。相比之下，表现出很少二色性的非α-螺旋结构则经历快速的H/D交换。发现先前被指定为β-折叠结构的1640 cm⁻¹处的谱带部分归因于视黄叉发色团质子化席夫碱的C = N伸缩振动。我们得出结论，细菌视紫红质的跨膜区域主要由α-螺旋结构组成，而大多数β型结构位于可直接接触水的表面区域。
