Bovine corneal Descemet's membrane (DM) was subjected to limited pepsin digestion.
Soluble native collagens were fractionated by differential salt precipitation, and
a mixture of type V collagen and collagenous fragments with a chain Mr of 50,000 (50K)
was obtained at a concentration of 1.5 M NaCl. Further purification of the 50K collagen
by molecular sieve and high-performance liquid chromatography resulted in the isolation
of two-non-disulfide-bonded polypeptides, 50K-A and 50K-B, which were susceptible
to several neutral proteases, including bacterial collagenase. By the criteria of
peptide mapping, amino acid composition, and N-terminal sequence analysis, 50K-A and
50K-B were structurally dissimilar, although both chains contained Gly-X-Y repeats.
50K-A and 50K-B were immunologically and structurally distinct from collagen type
I, III, IV, V, and VI. Immunohistochemical studies of bovine ocular tissue showed
preferential distribution of the collagen containing the 50K fragment in the DM, with
a more disperse arrangement of apparently interconnecting fibrils in the corneal stroma.
Type VIII collagen isolated from the culture medium of metabolically radiolabeled
bovine corneal endothelial (BCE) cells and its pepsin-resistant Mr 50 000 domain(s)
both cross-reacted with antisera to 50K polypeptides from the corneal DM. Additionally,
the CNBr peptide maps of pepsin-resistant Mr 50 000 polypeptides of type VIII collagen
isolated from BCE cells and bovine corneal DM were highly similar.(ABSTRACT TRUNCATED
AT 250 WORDS)