Basement membrane collagen synthesis by rabbit corneal endothelial cells in culture. Evidence for an alpha chain derived from a larger biosynthetic precursor.

Corneal endothelial cells in culture synthesize basement membrane collagen and secrete it into the medium. This collagen sediments faster than interstitial collagen by velocity sedimentation and is disulfide-bonded. After reduction, two biochemically distinct chains can be determined by cyanogen bromide peptide mapping. These chains migrate close to each other and immediately below beta 12(I) components on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Treatment with pepsin gives rise to a major band which still retains interchain disulfide bonds and which will not convert to components with the mobility of interstitial alpha chain by reduction. However, an alpha chain and three minor collagenase-sensitive and pepsin-resistant peptides are generated if the molecule is reduced and alkylated under nondenaturing conditions prior to pepsin treatment. When collagen which accumulates in the media over a long period of time is compared to the newly synthesized molecules, there is an apparent differential resistance to limited pepsin treatment. However, the products which are generated in both cases share electrophoretic identity.