Identification of type II procollagen in rabbit vitreous

A procollagen in the soluble fraction of rabbit vitreous was isolated by dialysis against dilute acetic acid and partially purified by Bio-Gel A 5M gel filtration. The molecule was identified to be type II procollagen by comparing its segment-long-spacing (SLS) banding pattern with that of standard type II collagen isolated from rabbit articular cartilage. Electron microscopy of the SLS of this type II procollagen revealed a fuzzy propeptide extension at the N-terminal end of the molecule. Pepsin digestion of the procollagen removed this extension, thus converting the molecule into a collagen which had mobility similar to that of pepsin-soluble cartilage type II collagen in SDS-polyacrylamide gel electrophoresis. No inter-chain disulfide bond was found in the propeptide extension when the procollagen samples were electrophoresized with or without mercaptoethanol. Comparison of the cyanogen bromide peptide map of the type II procollagen with that of the pepsin-soluble type II collagen indicated that two extra peptides were present in the digest of procollagen. All of this evidence suggested that the procollagen in the soluble vitreous body of the rabbit eye was a novel type II procollagen with a propeptide extension only at the N-terminus.