19] Estimation of the size of collagenous proteins by electrophoresis and gel chromatography

Abstract

Collagenous polypeptides have apparent low electrophoretic mobilities compared to those of typical globular proteins when their molecular weights are examined as a function of mobility. If, however, the number of amino acid residues epr polypeptide chain is examined as a function of electrophoretic mobility, both collagenous polypeptides and globular proteins obey the same empirical linear relationship. The relationship suggests that the number of residues in collagenous polypeptides from sources such as basement membranes, which may contain both collagenous and noncollagenous regions, may be estimated accurately from SDS-gel electrophoresis. Calf skin collagen and its naturally occurring cross-linked multimers, as well as polypeptides derived from it, provide useful molecular standards in a range from 150 residues to 11,500 residues per polypeptide chain (corresponding to a molecular weight range from 13,500 to about 1,000,000 for collagen). The number of residues can in turn be translated into molecular weight values with a knowledge of the mean residue weight of the polypeptide of interest. In contrast, the molecular weight of collagenous chains can be directly estimated by gel chromatography in Sepharose CL-4B, since collagen chains give the correct molecular weight when compared to globular protein standards.