The denaturation of acetic acid-soluble calf-skin collagen. Changes in optical rotation, viscosity and susceptibility towards enzymes during serial denaturation in solutions of urea

Abstract

Serial urea-denaturation of soluble calf-skin collagen dissolved in 0.1 M-acetic acid has been described. The reaction course has been followed by measuring the changes in laevorotation, viscosity and enzyme digestibility (after dialysis) of the protein dissolved in 0-1 M-acetic acid in the presence of increasing concentrations of urea. Soluble collagen has been denatured to produced gelatins of similar physical properties by either heat- or urea-depolymerization. This observation supports the previous claim by the authors that the thermal conversion of collagen into gelatin at neutral pH is a physical depolymerization accompanied by the rupture of only a minimal number of peptide bonds. Urea-depolymerization of soluble collagen to form a gelatin proceeds by the rupture of hydrogen bonds in two distinct steps. The first step involves the rupture of intermolecular hydrogen bonds. The second step is irreversible at pH 3.5 and involves the rupture of intramolecular hydrogen bonds with the consequent destruction of the collagen triple-helix structure and the formation of gelatin. The influence of inter-and intra-molecular hydrogen bonds on the resultant viscosity of dilute solutions of collagen were approximately equal under the conditions studied in this work.