Biosynthesis of procollagen [(pro alpha 1 V)2 (pro alpha 2 V)] by chick tendon fibroblasts and procollagen (pro alpha 1 V)3 by hamster lung cell cultures.

9%24Chick embryo tendon fibroblasts were cultured with [3H]amino acids for 4, 8, and 24 h.Procollagen V was found in the cell layer.The chain composition predominantly corresponded to [(proal V), prorv2 VI, and a small proportion existed as the disulfide-linked heterotrimer and dimer.It was progressively converted to p-collagen V and collagen V which were found both in the cell layer and in the culture medium.Processing proceeded as previously described for chick tissues including the attachment of a noncollagenous peptide-P to the pa2 V chain.The smallest chains were also larger than a V(pepsin).Cultures of Chinese hamster lung cells (clone HT1) synthesized the homotrimer (proal V)s.This lacked intermolecular disulfide bridges, was not processed, and remained associated with the cell layer.The chick fibroblast-conditioned culture media contained an enzymatic activity which converted procollagen V of blood vessels to p-collagen V.This p-collagen V lacked the noncollagenous peptide-P which is normally found associated by disulfide linkage to the pa2 V chain.This enzymatic activity also converted the hamster cell (proal V), to p-collagen V. Arginine inhibited this processing step.We conclude that the processing of procollagen V occurs extracellularly, is defective in the hamster lung cell cultures and that the type V molecules remain largely associated with the cell layer.The previously proposed parallel biosynthesis of homo-and heteroprocollagens V, and their subsequent processing in tissues are consistent with the present results.In several preceding publications (1-3), we concluded that type V collagen is made in several chick tissues as a mixture of procollagens representing [(proal V)z(proa2 V)] and (proal V):j.An initial relatively fast processing step from procollagen V to p-collagen V is followed by a slow conversion to collagen V. To dissect these processes further we turned to cell culture.Information on extracellular processing steps can be obtained by separate analyses of the cell layer and the conditioned culture media.Fibroblast cultures from several chick tissues (4-8) and cultures of other cell types (9-14) have been shown to synthesize type V collagenous proteins.Chick tendon fibroblast cultures synthesize and secrete types I, 111, and V collagenous proteins.