Proteoglycans synthesized by articular and epiphyseal chondrocytes in culture were compared. Proteoglycans extruded by the two types of cells into the culture medium are of identical M r. On the other hand, the proteoglycans of cells or pericellular matrix synthesized by the articular chondrocytes are characterized by an heterogeneous fraction of low-M r which is not present in the material derived from epiphyseal chondrocytes. There are at least two components in this fraction: the first seems to be a precursor of aggregated proteoglycans, the other may represent a component of cell coat. Stimulation of the cell cultures with vitamin D metabolites and somatomedin enhances proteoglycan biosynthesis but no modification is observed in the proteoglycan M r.
