Ultracentrifugation as a probe of conformation of unhydroxylated procollagen and collagen

Unhydroxylated and hydroxylated procollagen and collagen were compared by zone velocity and isopycnic centrifugation. The sedimentation coefficient of unhydroxylated procollagen(3.7 S) was slightly less than that of hydroxylated procollagen (3.9 S) and the sedimentation coefficient of unhydroxylated collagen (2.9 S) was slightly less than hydroxylated collagen (3.2 S). These differences could be accounted for largely by the slight increase in molecular weight and density of the hydroxylated molecules. The results indicate that the unhydroxylated molecules are in a triple helical conformation composed of three chains rather than analogous helical structures formed by the back-folding of individual chains. We conclude, therefore, that previous experiments demonstrating the decreased thermal stability of unhydroxylated collagen relative to hydroxylated collagen have measured the denaturation of true triple helices.