Thermodynamic and structural characteristics of collagen fibrils formed in vitro at different temperatures and concentrations

Analysis of the results of calorimetric study of reconstituted collagen (type I) fibrils, in particular, the half-width of the temperature transition, shows that the collagen packing density in the fibrils and the size of cooperative blocks therein depend on the assembly temperature and on the initial collagen concentration. The least dense fibrils are formed at subphysiological temperatures (25° or 30°C) and low concentration (0.3 mg/ml). The extent of ordering does not change upon doubling the concentration but increases upon quadrupling it. At physiological temperature (35°C) the fibrils are densely packed regardless of collagen concentration. The enthalpy of fibril assembly is minimal at 35°C, 1.2 mg/ml, and ionic strength of 0.17 M. The influence of temperature on particular steps of fibrillogenesis and the role of water in these processes are discussed.