Arvinte T, Drake A F
Ciba-Geigy Pharmaceuticals, Horsham, United Kingdom.
J Biol Chem. 1993 Mar 25;268(9):6408-14.
Molecular conformations of salmon (sCT) and human (hCT) calcitonin in media with different concentrations of methanol/water and trifluoroethanol/water have been investigated by fluorescence, circular dichroism (CD) and infrared spectroscopy techniques. In these media, sCT and hCT adopt an alpha-helical structure comprising up to 40-48% of the amino acids. CD experiments reveal that for both peptides, the ordering of the Cys1-Cys7 disulfide link and the alpha-helix formation can be distinguished. Disulfide bond ordering is similar in both calcitonins. sCT adopts the alpha-helical structure more readily than hCT, as solvent polarity is reduced. In 2,2,2-trifluoroethanol (TFE)/water mixtures the alpha-helix formation for both hCT and sCT is a two-step process. The first alpha-helix formation step occurs at lower TFE concentrations (less than 11 mol% TFE for hCT and 6 mol% TFE for sCT). The second alpha-helix formation step represents 50 and 23% of the whole conformational change for hCT and sCT, respectively. Tyrosine fluorescence measurements correlate with the far ultraviolet CD changes associated with the peptide backbone. hCT is seen to adopt a left-handed, extended conformation in aqueous media below -50 degrees C.
利用荧光、圆二色性（CD）和红外光谱技术，研究了鲑鱼降钙素（sCT）和人降钙素（hCT）在不同浓度甲醇/水和三氟乙醇/水介质中的分子构象。在这些介质中，sCT和hCT采用α-螺旋结构，其中氨基酸含量高达40%-48%。CD实验表明，对于这两种肽，可以区分Cys1-Cys7二硫键的有序排列和α-螺旋的形成。两种降钙素中二硫键的有序排列相似。随着溶剂极性的降低，sCT比hCT更容易形成α-螺旋结构。在2,2,2-三氟乙醇（TFE）/水混合物中，hCT和sCT的α-螺旋形成都是一个两步过程。第一个α-螺旋形成步骤发生在较低的TFE浓度下（hCT为低于11 mol% TFE，sCT为6 mol% TFE）。第二个α-螺旋形成步骤分别占hCT和sCT整个构象变化的50%和23%。酪氨酸荧光测量结果与肽主链相关的远紫外CD变化相关。在低于-50℃的水性介质中，hCT呈现左手伸展构象。
