three-bond isotope shifts. By virtue of the well-separated signals, the proton/deuteron fractional factors for both the SH and amide groups of the two Cys residues in EPPIb could be directly determined, as approximately 0.4-0.5 for [SD]/[SH] and 0.9-1.0 for [ND]/[NH], by the relative intensities of the NMR signals for the isotopomers. The proton NOE's of the two slowly exchanging SH's were clearly identified
已经开发了一种用于识别具有氢交换速率缓慢的巯基 (SH) 基团的半胱
氨酸 (Cys) 残基的方法,用于
水性介质中的蛋白质。该方法利用由 SH 基团的
氘化引起的 C(β)
化学位移的同位素位移。用 [3-(13)C;3,3-(2)H(2)]Cys 选择性标记的 18.2 kDa 大肠杆菌肽基脯
氨酰顺反异构酶 b (EP
PIb) 显示出更窄的线宽(13)C(beta) NMR 信号,与用 [3-(13)C]Cys 或 (3R)-[3-(13)C;3-(2)H] 标记的蛋白质相比半胱
氨酸。EP
PIb的两个Cys残基即Cys-31和Cys-121的(13)C(β)信号,用[3-(13)C;3,3-(2)H(2)]Cys标记,在 40 摄氏度和 pH 7.5 下,在 H(2)O/D(2)O (1:1) 中分成四个信号,表明侧链 SH' 的交换率 由于二键和三键同位素位移,s 和主链酰胺太慢而无法平均