The presence of intermolecular disulfide cross-links in type III collagen.

Bovine and lathyritic rat type III collagen preparations were analyzed for the presence and in vitro formation of intermolecular disulfide cross-links. Type III collagen from fetal bovine skin was extracted with the aid of pepsin and purified by differential salt precipitation, guanidine denaturation, and renaturation. Nearly all of the type III collagen was present as reduction-sensitive gamma-components and higher molecular weight aggregates. After cleavage with CNBr, the peptides were analyzed by two-dimensional mapping. The presence of intermolecular disulfide bonds was demonstrated by the existence of a hexamer of the COOH-terminal CNBr peptide, CB9B. This cross-linked peptide was completely converted to the CB9B monomer by reduction. Type III collagen from the skins of beta-aminoproprionitrile-treated rats was used to test for the in vitro formation of intermolecular disulfide cross-links. This was prepared by salt extraction, differential salt precipitation, and pepsin treatment. Sodium dodecyl sulfate-gel electrophoresis of this partially purified type III collagen before reconstitution into fibers detected primarily gamma-chains. After reconstitution into fibers, the majority of the material was present as higher molecular weight aggregates. Upon reduction, these aggregates generated predominantly alpha-chains. These data demonstrate the existence of intermolecular disulfide bonds in native type III collagen and their formation during in vitro fibrillogenesis.