Biosynthesis of chondroitin sulfate: Microsomal proteoglycans

A microsomal preparation from chick embryo epiphyseal cartilage was incubated with UDP-¹⁴C]glucuronic acid and UDP-N-acetylgalactosamine to form ¹⁴C] chondroitin-labeled proteoglycan. Two ¹⁴C]proteoglycan populations were obtained which differed in size, ¹⁴C]glycosaminoglycan content, and susceptibility to alkali. One population of ¹⁴C]proteoglycan appeared near the void volume on Sepharose 2B, while the other population was smaller, similar in size to monomer proteoglycan. The larger ¹⁴C]proteoglycan contained long ¹⁴C]chondroitin chains added to short primers; these chains were in part resistant to alkali cleavage from protein. The smaller ¹⁴C]proteoglycan contained mainly ¹⁴C]chondroitin chains of intermediate length added to endogenous chondroitin sulfate; these chains were all susceptible to alkali cleavage from protein. The larger ¹⁴C]proteoglycan may represent a precursor proteoglycan present at the site of glycosaminoglycan chain synthesis.