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

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(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.