Biosynthesis of Cartilage Procollagen

Cells were isolated by controlled enzymic digestion of sternal cartilages from chick embryos and the cells were studied immediately after isolation for up to 4 h in vitro. The cells isolated under the conditions employed had a high degree of viability, they remained in suspension for 2 to 4 h in vitro and during this time they synthesized and secreted collagen in the precursor form which has been called “transport form” or “procollagen”. The cells also incorporated [35S]sulfate into macromolecules which were secreted into the medium.Continuous labeling of the cartilage cells demonstrated a lag of about 33 min between the time at which the rate of synthesis of collagen [14C]hydroxyproline became linear and the time at which the secretion of collagen [14C]hydroxyproline into the medium became linear.Gel filtration and polyacrylamide‐gel electrophoresis in sodium dodecylsulfate indicated that all the secreted collagen was in the precursor form. The procollagen differed from the procollagen previously isolated from bone, tendon and cultured fibroblasts in that it apparently consisted of a single type of polypeptide chain. Isotopic studies suggested that the NH2‐terminal extension on th