Bovine cartilage types VI and IX collagens. Characterization of their forms in vivo

Abstract

Collagens were extracted from bovine cartilage by 4 M-guanidinium chloride in the presence of proteinase inhibitors and identified by immunoblotting with specific anti-collagen sera. The collagens retained their native conformations (shown by the resistance of their triple-helical domains to pepsin digestion), and the molecular masses of their component α-chains indicated that the chains were intact. Type VI collagen was extracted as a large-molecular-mass disulphide-bonded aggregate composed of components of molecular mass 140 kDa and 200-240 kDa, and was therefore similar to type VI collagen identified in non-cartilaginous tissues. Immunoblotting established the 200-240 kDa components as intact forms of the α(VI) chain. Type IX collagen consisted of three clearly separable components of molecular mass 84 kDa, 72 kDa and 66 kDa which were assigned to the α1(IX)-, α3(IX)- and α2(IX)-chains respectively, and a large proportion of this collagen had no covalently bound glycosaminoglycan attached to the α2(IX)-chain. Differences between the type IX collagen extracted from bovine cartilage and that identified in biosynthetic studies on chick cartilage are discussed.