Jap B K, Maestre M F, Hayward S B, Glaeser R M
Biophys J. 1983 Jul;43(1):81-9. doi: 10.1016/S0006-3495(83)84326-4.
Ultraviolet circular dichroism spectroscopy in the interval from 190 to 240 nm and infrared spectroscopy in the region of the amide I band (1,600 cm-1 to 1,700 cm-1) has been used to estimate the alpha-helix content and the beta-sheet content of bacteriorhodopsin. Circular dichroism spectroscopy strongly suggests that the alpha-helix content is sufficient for only five helices, if each helix is composed of 20 or more residues. It also suggests that there is substantial beta-sheet conformation in bacteriorhodopsin. The presence of beta-sheet secondary structure is further suggested by the presence of a 1,639 cm-1 shoulder on the amide I band in the infrared spectrum. Although a structural model consisting of seven alpha-helical rods has been generally accepted up to this point, the spectroscopic data are more consistent with a model consisting of five alpha-helices and four strands of beta-sheet. We note that the primary amino acid sequence can be assigned to segments of alpha-helix and beta-sheet in a way that does not require burying more than two charged groups in the hydrophobic membrane interior, contrary to the situation for any seven-helix model.
利用190至240纳米区间的紫外圆二色光谱以及酰胺I带区域（1600厘米-1至1700厘米-1）的红外光谱来估算细菌视紫红质的α-螺旋含量和β-折叠含量。圆二色光谱强烈表明，如果每个螺旋由20个或更多残基组成，那么α-螺旋含量仅足以形成五个螺旋。它还表明细菌视紫红质中存在大量的β-折叠构象。红外光谱中酰胺I带出现1639厘米-1的肩峰进一步表明存在β-折叠二级结构。尽管由七个α-螺旋杆组成的结构模型在此之前一直被普遍接受，但光谱数据与由五个α-螺旋和四条β-折叠链组成的模型更为一致。我们注意到，与任何七螺旋模型的情况相反，一级氨基酸序列可以以一种不需要在疏水膜内部掩埋超过两个带电基团的方式分配到α-螺旋和β-折叠片段中。
