Metabolism of a cartilage matrix glycoprotein in normal and osteoarthritic canine articular cartilage.

We have recently described a 550,000-dalton noncollagenous cartilage matrix glycoprotein (CMGP), with subunits of 130,000, which is present in hyaline cartilage and fibrocartilage. Biosynthetic studies indicated that CMGP was synthesized by short-term organ cultures of normal canine articular cartilage, representing approximately 9% of the total 3H-leucine incorporated into protein in 24-hour cultures. There was no incorporation of 35S-sulfate or 3H-mannose into CMGP under these conditions, but the protein did incorporate 32P-phosphate. The majority of the 3H-leucine-labeled CMGP was removed after 24 hours of chase with unlabeled leucine, and only a small amount remained at 72 hours, which suggests that there was rapid metabolism of the protein. CMGP was not detected in cartilage after addition of cycloheximide to the culture medium; this confirms its short half-life. Cultures of osteoarthritic cartilage obtained from dogs 8-10 weeks after anterior cruciate ligament transection revealed no difference in the metabolism of CMGP in this tissue compared with that found in cultures of normal articular cartilage.