ISOLATION OF BOVINE TYPE-X COLLAGEN AND IMMUNOLOCALIZATION IN GROWTH-PLATE CARTILAGE

Type X collagen was extracted with 1 M-NaCl and 10 mM-dithiothreitol at neutral pH from fetal-bovine growth cartilage and purified to homogeneity by using f.p.l.c. gel filtration on a Superose 12 column, followed by ion-exchange chromatography on a Mono Q column. The purified protein migrates in SDS/polyacrylamide gels with an apparent M(r) of 58 000 under reducing conditions and as high-M(r) oligomer in its unreduced form. The amino acid composition is similar to the published composition of chick type X collagen. Pepsin digestion at 4 °C decreased the M(r) of the monomer to 43 000; purified bacterial collagenase digests most of the molecule, leaving a non-collagenous domain of apparent M(r) 15 000, which probably represents the C-terminal globular domain. The IgG fraction from a rabbit antiserum raised against purified bovine type X collagen was specific for this collagen by the criteria of e.l.i.s.a. and immunoblotting after immunoabsorption with collagen types I, II, IX and XI. Immunofluorescence localization of type X collagen in sections of fetal-bovine and human cartilage was possible after acetone fixation of sections and hyaluronidase treatment. Type X collagen was restricted to the zone of hypertrophic and calcified cartilage inside the bone spicules of the growth plate.