Abstract
Interpreting the data of Kobayashi et al.^1^ on the thermal transitions of triple helices of (gly‐pro‐pro)~n~ for n = 10, 15, and 20 using a simple model of unzippering and chain dissociation, the thermodynamic parameters characterizing gly‐pro‐pro triple‐helix formation have been determined. The enthalpy and entropy of triple‐helix formation per repeating unit are found to be −7.4 ± 0.8 kcal/mol and −20 ± 2 eu, respectively. Using these parameters, the nature of the unwinding has been investigated for chains containing up to 300 triplets; it is found that there is only a minor amount of helix unwinding from the ends, the major change in helical content arising from chain dissociation. Experimental data on the melting temperatures of natural collagens as a function of imino‐acid composition are used together with the thermodynamic parameters for (gly‐pro‐pro)~n~ to estimate the thermodynamic parameters for triple‐helix formation of amino versus imino acids (the parameters for the former being found to be similar to those for α‐helix formation). Calculations are given using these parameters for model specific‐sequence collagens; it is found that heterogeneity can have a significant influence on the nature of the unwinding of the triple helix.