On the mechanisms of the effect of imino acids on the physical characteristics of collagens

The effect of imino acids on thermodynamic characteristics of the collagen-type structures in collagens from different sources is analyzed. It is demonstrated that the main mechanism of the entropy increase in the system water-protein with an increase in the imino acid content in a polypeptide chain is a change in the number of cooperative regions, detectable during the melting of a fibrous macromolecule. The variation of physical characteristics of the cooperative units determines, in particular, the variation of the hydrogen bond parameters, which appears as a broadening of the bands of NH valence vibrations and the half-widths of transitions in postdenaturation structures. Thus, the main mechanism of how imino acids act on the thermodynamic characteristics of collagens is connected with a complex nature of the denaturation process, when any substitutions of imino acids for amino acids significantly change the dehydration-hydration of the native and denatured states.