| Abstract: | Studies of collagen synthesis by specific sections of individual fetal bovine costochondral junction growth plates were conducted and histologically related to the zones from which the sections were derived. Sections were metabolically labeled in organ culture to examine the synthesis of collagen and its precursors. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that Type II collagen was the major species synthesized in all tissue sections; 1 alpha, 2 alpha, 3 alpha collagen chains were synthesized in all growth plate sections and to a small extent in the fetal structural cartilage. A short chain collagen was synthesized predominantly in the zones of degeneration and provisional calcification and accounted for 8-12% of the radioactivity in this section. This short chain collagen has 63-kDa subunits which are converted to 46-kDa species by limited proteolysis with pepsin. Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis demonstrated that both the pepsin- and non-pepsin-treated forms of short chain collagen are disulfide-bonded. Digestion with bacterial collagenase showed that the 46-kDa and a major portion of the 63-kDa forms are collagenous. Pulse-chase studies in organ culture did not demonstrate an obvious precursor to the 63-kDa form, and there was no conversion to the 46-kDa after 20 h. Synthesis of short chain collagen appears to be specific to the process of endochondral ossification in the growth plate; its appearance may be critical to this transition process. |
