Heterogeneity of pepsin-solubilized human glomerular basement membrane collagen

The collagen component of isolated glomerular basement membrane ws solubilized by limited pepsin digestion and further purified. The amino acid and carbohydrate composition of the final material was very similar to that described for the alpha1-chains of type IV collagen. However, the presence of several components was detected when the material was analyzed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis either without or after reduction. The molecular weights of the major components in the reduced material were about 140,000, 100,000, 80,000 and less than 65,000 (in the case of five components). The data thus do not support the previous suggestion that the human glomerular basement membrane contains only one type of collagen polypeptide chain. However, part of the heterogeneity may be due to the presence of more than one collagenous part in a procollagen-type polypeptide chain, and an additional reason may lie in a partial degradation of collagenous portions during pepsin digestion.