BIOSYNTHESIS AND CHARACTERIZATION OF TYPE-X COLLAGEN IN HUMAN FETAL EPIPHYSEAL GROWTH-PLATE CARTILAGE

We examined in vitro collagen biosynthesis by organ cultures from huma n fetal epiphyseal growth plate cartilage. The biosynthetic products w ere characterized by NaCl fractional precipitation, limited proteolyti c digestion, and sodium dodecyl sulfate-polyacrylamide slab gel electr ophoresis. Organ cultures of human fetal epiphyseal growth plate carti lage synthesized large amounts of type X collagen in addition to type II, type IX, and type XI collagens. The individual polypeptide chains of human type X collagen migrated with an apparent M(r) of 45 kDa afte r proteolytic digestion with pepsin. The migration pattern of these mo lecules did not change when examined under reducing and nonreducing co nditions, indicating that they did not contain intrahelical disulfide bonds. Comparison of the rates at type X collagen biosynthesis at week s 20 and 24 of human fetal development showed a marked increase of 24 weeks. Northern hybridization analysis of total RNA from freshly isola ted epiphyseal growth plate chondrocytes with a cDNA corresponding to the carboxyl terminus of human type X collagen indicated that the deve lopmental increase of type X collagen production is determined by pre- translational mechanisms.