Rico M, Gallego E, Santoro J, Bermejo F J, Nieto J L, Herranz J
Biochem Biophys Res Commun. 1984 Sep 17;123(2):757-63. doi: 10.1016/0006-291x(84)90294-8.
The fundamental role of the Glu 2- ... Arg 10+ salt bridge in the folding of isolated S-peptide (1-19 N-terminal fragment of Ribonuclease A) is demonstrated from the comparison of the helix contents, at 0 degrees C, of S-peptide and related peptides. Helix contents have been determined from the analysis of proton chemical shift vs. temperature curves. The observed data can be accounted for by assuming that two side-chain interactions contribute to stabilize the 3-13 helix of S-peptide, the salt bridges Glu 2- ... Arg 10+ and Glu 9-... His 12+, the former being more effective. The salt bridge Glu 9- ... Arg 10+ turns to a weaker interaction, a hydrogen bond Glu 2 (C delta = 0) ... Arg 10+, on protonation or esterification of the Glu 2 carboxylate.
通过比较0℃下S肽（核糖核酸酶A的1-19 N端片段）及相关肽段的螺旋含量，证明了Glu 2-... Arg 10+盐桥在孤立S肽折叠过程中的基本作用。螺旋含量是通过分析质子化学位移与温度曲线来确定的。观察到的数据可以通过假设两种侧链相互作用有助于稳定S肽的3-13螺旋来解释，即盐桥Glu 2-... Arg 10+和Glu 9-... His 12+，前者更有效。当Glu 2羧酸盐质子化或酯化时，盐桥Glu 9-... Arg 10+转变为较弱的相互作用，即氢键Glu 2（Cδ=0）... Arg 10+。
