A short chain (pro)collagen from aged endochondral chondrocytes. Biochemical characterization

After 5 weeks in secondary culture, chondrocytes derived from specific regions of the embryonic chick tibiotarsus secrete greater than 90% of their culture medium collagen as a short chain (SC) collagen. Quantities of the molecule, sufficient for biochemical characterization, were isolated without proteolytic treatment from the medium of such mass cell cultures. The chains, Mr = 59,000, of SC collagen are cleaved to Mr = 45,000 by limited pepsin digestion of the native molecule. These two forms of SC collagen are referred to as the 59K form and the 45K form. The CD spectrum of the 59K form confirms the presence of a triple helical domain within the molecule. The amino acid composition of the two forms of SC collagen show it to be different from any other known collagen, including the short chain collagens that have been isolated by the proteolytic extraction of cartilages. The most characteristic features of SC collagen are its high content of methionine, low level of arginine, and a lack of cysteine. The amino acid composition of the 45K form shows it to be the collagenous domain, while the differences between the 45K and 59K form presumably reflect the composition of the nonhelical domain of the 59K form. The nonhelical domain contains greatly elevated levels of aromatic amino acids which contribute to the hydrophobic character of this domain.