Propeptides of procollagen V (A,B) in chick embryo crop

The biosynthesis of type V (A,B) collagens was recently found to proceed through the sequential forms pro alpha (A,B), p alpha (A,B), and f alpha (A,B). All these chains are larger than the A,B chains extracted from tissues after pepsin digestion. This report shows that all forms contain substantial peptides which are resistant to bacterial collagenase and concludes that type V collagens differ from the intestitial collagens (types I, II, III) in retaining large noncollagenous peptides in tissues. A peptide becomes transiently attached to the processing intermediate p alpha A by a reducible linkage. The conversion of procollagen V to p-collagen V was inhibited by colchicine and arginine. Previously, the disulfide-linked heterotrimer [(pro alpha B)2 (pro alpha A)] was found and additional procollagens containing only B type molecules were inferred. Further investigations reported here agree with these conclusions and also indicate that some trimeric molecules containing more than one chain related to A may exist.