Isolation, chemical and electron microscopical characterization of neutral-salt-soluble type III collagen and procollagen from fetal bovine skin.

Extraction of fetal bovine skin at neutral pH and in the presence of protease inhibitors solubilized substantial amounts of type I and type type III collagen and Type III procollagen. Type I and Type III collagen were separated from each other by salt precipitation, and DEAE-cellulose chromatography was used to separate collagen from procollagen. The main chain constituents in type III collagen and procollagen were disulfide-bonded gamma and pgamma components, respectively. Amino acid composition, cross striation banding as observed using electron microscopy, cyanogen bromide peptide patterns in disc electrophoresis gels and resistance of the disulfide regions to pepsin digestion indicated a close similarity to previously described insoluble type III collagen, which was solubilized by limited pepsin digestion. Electron microscopy of long-spacing-segment crystallites and evidence for an extended form of the disulfide-bonded cyanogen bromide peptide suggested that neutral-salt-soluble type III collagon is longer at its C-terminal end by about 10 to 20 amino acid residues than pepsin-treated material. A small elongation was also indicated in the N-terminal portion of the molecule. Procollagen has an additional N-terminal extension with a length of about 160 A, but no difference was observed between collagen and procollagen at their C-terminal ends.