Phosphorylation of Proteoglycans in Human Articular Cartilage

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Abstract
A study of human articular cartilage indicated that component proteoglycans can be phosphorylated. Phosphoryla-tion, also found in a specimen of human epiphysial cartilage, occurred when [γ-32P]-ATP or 32P1 was included in the in vitro incubation medium. Treatment of the phosphorylated proteoglycans with chondroitinase and chondro-sulfatases effectively removed the chondroitin sulfate without dephosphorylating the remaining molecule. Since phosphorylation could be effected in a totally chemically defined medium, it appears that the necessary enzyme systems for this reaction are contained entirely within chondrocytes.