| Abstract: | The thermal triple helix–coil transition of covalently bridged collagenlike peptides with repeating sequences of (Ala-Gly-Pro)n, n = 5–15, was studied optically. The peptides were soluble in water/acetic acid (99:1) and were found to form triple-helical structures in this solvent system beginning with n = 8. The thermodynamic analysis of the transition equilibrium curves for n = 9–13 yielded the parameters ΔH°s = ?7.0 kJ per tripeptide unit, ΔS°s = ?23.1 J deg?1 mol?1 per tripeptide unit for the coil-to-helix transition, and the apparent nucleation parameter σ ? 5 × 10?2. It was suggested through double-jump temperature experiments that the rate-limiting step during refolding is not only influenced by the difficulties of nucleation, but also by cis–trans isomerization of the Gly-Pro peptide bond. |
