Kinetics of collagen denaturation in mammalian lens capsules studied by differential scanning calorimetry.

Calorimetry was used to measure the rates of irreversible denaturation of collagen in intact mammalian lens capsules, isothermally stored in water at different temperatures, and the kinetic characteristics of the process determined. At 47.4 degrees C, the number of native collagen molecules declined by a factor of 10 in 21.4 +/- 2.9 min (this is called the D-value) and increasing the storage temperature by 2.32 +/- 0.12 degrees C reduced the D-value by a factor of 10. The activation energy of the process was 860 +/- 44 kJ mol-1, and the activation enthalpy and entropy were respectively 858 +/- 45 kJ mol-1 and 2.38 +/- 0.14 kJ mol-1 K-1. Using equations derived in the paper, these kinetic characteristics were used to predict the position and shape of the denaturation endotherms over a range of scanning rates. Comparison of the predicted and actual positions of peak maxima showed a close correspondence, demonstrating that the principal phenomenon determining the position of the peak maxima was an irreversible rate process. While there was fairly good agreement between the predicted and actual shape of the endotherm at low scanning rates, measurements at high rates were distorted by the finite response time of the calorimeter, and the agreement was poor.