Kinetics of the helix/coil transition of the collagen-like peptide (Pro-Hyp-Gly)10

This article measures the rates of folding and unfolding of the collagen-like peptide (Pro-Hyp-Gly)(10) over overlapping concentration and temperature ranges. The data allow calculation of the orders of the folding and the unfolding reactions, the effective Arrhenius activation energies, and numerical solution of the differential equation controlling the helix/coil transition during temperature scanning. The resulting predictions of helicity closely followed DSC measurements of the peptide in both up- and down-scanning modes, confirming the validity of the theoretical equations governing the kinetics of the folding/unfolding process. In both up- and down-scanning, three regions were apparent: "quasistatic," "rate," and "mixed." At very low scanning rates, a quasistatic region revealed a broad, short endotherm that was independent of scanning rate, but dependent on concentration and equal to the equilibrium endotherm. At high up-scanning rates, the "rate region" endotherm was sharp and tall and T(max) increased with scanning rate. In down-scanning, the "rate peak" was very broad and very short and T(max) decreased with scanning rate. The "mixed region" showed nascent "rate" and nascent "quasistatic" peaks, which were evident in the same up-scan under certain conditions. Comparison of (Pro-Hyp-Gly)(10) and (Pro-Pro-Gly)(10) showed that the higher temperature stability of (Pro-Hyp-Gly)(10) is due mainly to its slower rate of unfolding and higher activation energy.