Characterization of the collagenous domain of bovine glomerular basement membrane

Bovine glomerular basement membrane was subjected to limited pepsin digestion and the solubilized collagenous polypeptides were characterized. Several electrophoresis systems were used which enabled an examination over a molecular weight range from 20,000 to greater than 10(6). A 0.1% SDS-5% polyacrylamide gel system resolves the reduced digestion product into 17 polypeptides ranging in molecular weight from 78,000 to 340,000. The larger collagenous components were resolved on a 0.1% SDS-2.5% agarose gel system. The nonreduced digestion product resolves into 13 components which vary in molecular weight from 85,000 to 5 million. Upon reduction, the majority of this material is converted to a 165,000 molecular weight component(s) and cross-linked (aldehyde derived) multimers of this component(s) containing as many as 6 cross-linked monomers. The digestion product was subjected to a second pepsin digestion after reduction and alkylation under nondenaturing conditions. This results in a conversion of a larger polypeptides to three lower molecular weight peptides, two of which exhibit an electrophoretic migration identical to alpha 1- and alpha 2-chains of collagen. The results indicate that the collagenous domain of glomerular basement membrane consists of various size collagen molecules connected by disulfide bonds and aldehyde-derived cross-links to form high molecular weight aggregates containing as many as 30 of these polypeptides, and that the larger collagenous polypeptides contain alpha-size segments within their structure.