Collagen intrinsic viscosity

The intrinsic viscosity of the collagen preparation supports the notion that a significant fraction of the adsorbed collagen is present in the form of the dimer, i.e. of two triple helical, 3000 A long cylinders, flexibly joined together. Whereas at 7.7°C these dimers may mainly be folded and have two of the non-helical ends on the surface. It is conceivable that one end is permitted to lift off at the higher temperature and that the doubling in thickness is thus produced by a mechanism not related to a BET-like multilayer formation. 

Nishihara and Doty (200) have found that the intrinsic viscosities of a series of collagen samples degraded by sonic irradiation are well represented as those of prolate ellipsoids with Mjp = 2020, which corresponds to about 22 peptide residues. These figures resemble in magnitude those of poly(y-benzyl-L-glutamate) helices, and have been interpreted as confirmation of a three-stranded helical structure. 

Examination of Fig. 17 reveals that the temperature interval over which the transition takes place has a finite breadth, and thus may be characterized by various temperatures defined in different ways. Td, the temperature quoted in Table X, is defined as the temperature of the midpoint of the transition. If one assumes (1) that the fractional change in intrinsic viscosity (or specific rotation) is proportional to the fractional conversion of collagen from a single completely native state to a single completely denatured state, and (2) that equilibrium between these two forms is attained at every temperature, then the relation To = AH/AS applies and these thermodynamic parameters can be calculated from data such as... 

Nevertheless, solutions of molecules can be prepared from both types of tissue by extraction with weak acids or neutral salts. Structural changes due to heat can be conveniently followed in these solutions by observing changes in viscosity and optical rotation. The underlying assumption in such studies is that the molecules are free of interactions with one another in contrast to the close interaction in the solid native state. For most soluble collagens the specific rotation and intrinsic viscosity rj, of dilute neutral solutions are almost temperature independent, until a particular value is reached at which... 

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