The order-disorder transitions in fibrillar proteins. Stress-temperature dependence of hydrothermal contraction of the native collagen fibers

The melting of collagen in rat tail tendons tanned by p-benzoquinone has been investigated. It was shown that the degree of tannage if it is not too high does not influence the tension-temperature dependence. Our data indicate that the isometric tension-temperature curves determined at any heating rate are not equilibrium. However the curves obtained at a moderate heating rate after preliminary partial melting of the fiber are practically coincident with the thermodynamically equilibrium melting curve.

The rate of heating does not affect the relative contraction values derived from the isotonic length-temperature curves. Therefore the values of critical parameters of the melting, critical stress and critical temperature, estimated from the isotonic data and from the tension-temperature curves of partially premelted fibers are equilibrium. The theoretical equilibrium tension-temperature dependence was first calculated from the Flory equation for the melting in fibrous proteins under load using the experimentally determined value of critical temperature. The resulting curve coincides with the experimental equilibrium curve accurate within the estimation of the number of polymer chains per unit of fiber cross-section. The applicability of the approach used in this study for the analysis of melting of various natural and synthetic polymer fibers is discussed.