The mechanisms by which the transition temperature of triple helix to random coil is determined

(1)胶原蛋白模型肽（Pro-Pro-Gly）10在溶液中形成三螺旋。三重螺旋一直被认为是以单一状态存在的。在这项研究中，（Pro-Pro-Gly）10的三螺旋的两种状态进行了详细的研究，通过NMR。用NOESY和TOCSY谱对三螺旋中脯氨酸残基的亚甲基质子进行了完全的立体专一性归属。1H化学位移的温度依赖性表明，从HL到HH的热转变，即，HL-HH热转变可归因于第一脯氨酸（Pro 1）残基的构象变化。(2)用核磁共振方法研究了氘代醇对胶原蛋白模型肽（Pro-Pro-Gly）10在D_2O溶液中热转变的影响。1-在低醇浓度下，丙醇（d8）和异丙醇（d8）对（Pro-Pro-Gly）10热转变的影响与甲醇（d4）和乙醇（d 6）的影响不同，这是由于醇对这两种共存构象的影响不同所致.这些结果表明，在确定相变温度时，添加剂对变性构象的影响比对天然构象的影响更为重要，变性构象对添加剂的敏感性更高。

(1) A collagen model peptide, (Pro-Pro-Gly) 10, forms the triple helix in solution. The triple helix had always been considered to exist as a single state. In this study, two states of the triple helix of (Pro-Pro-Gly) 10 were investigated in detail by NMR. Complete stereospecific assignments of the methylene protons of the proline residues in the triple helix were *ccomplished by the use of NOESY and TOCSY spectra. The temperature dependence of the 1H chemical shifts showed that the thermal transition from the HL to the HH, i.e., the HL-HH thermal transition, can be attributed to the conformational change of the first proline (Pro1) residues.(2) The effects of deuterated alcohols on the thermal transition of a collagen model peptide, (Pro-Pro-Gly) 10, in D2O solution has been studied in detail by NMR. 1-propanol (d8) and 2-propanol (d8) showed effects quite different from that of methanol (d4) and ethanol (d6) on the thermal transition of (Pro-Pro-Gly) 10 at low alcohol concentration ; These were explained by considering different effects of alcohols on each of the two coexisting conformations. These results indicate in general that the effects of the additives on the denatured conformation which is more susceptible to additives are more important than that on the nature conformation in determining the transition temperature.