Identification of a disulfide-bonded 70 Kd type X procollagen in embryonic chick sternum cartilage

Chondrocytes from the presumptive calcification region of 20 day old embryonic chick sternum were found to synthesize a 70 Kd Type X procollagen precursor in addition to the previously described 59 Kd Type X collagen molecules. The 70 Kd molecules exhibited an additional cyanogen bromide peptide, contained a disulfide-bonded domain, and were converted into the 59 Kd moieties during pulse-chase experiments. The conversion of the 70 Kd to the 59 Kd Type X collagen was prevented upon microtubular transport inhibition with colchicine and resulted in tissue accumulation of the 70 Kd Type X procollagen.