Biosynthesis of the Chondroitin Sulfate Proteoglycan: PURIFICATION AND PROPERTIES OF XYLOSYLTRANSFERASE

Abstract

Abstract Xylosyltransferase from embryonic chick epiphyseal cartilage catalyzes the transfer of xylose from UDP-xylose to particulate endogenous acceptors or to an exogenous protein acceptor obtained by Smith degradation of bovine chondroitin sulfate-protein complex. Use of the exogenous protein acceptor enabled determination of enzymic activity independently of endogenous acceptors. Homogenization of cartilage in buffers containing from 0.2 to 1 m KCl followed by centrifugation at 105,000 x g yielded soluble fractions which contained from 65 to 95% of the xylosyltransferase activity. The remainder of the activity was associated with the 105,000 x g sediment. Soluble enzyme was fractionated with ammonium sulfate and purified by centrifugation on density gradients or by gel filtration resulting in a 50-fold purification. The specific activities of xylosyltransferase in embryonic chick cartilage, brain, liver, and intestine were compared; enzyme activity was highest in cartilage. The specific activity of the transferase in brain was 8% of that from cartilage, whereas liver and intestine exhibited no measurable activity with the exogenous acceptor. Xylosyltransferase catalyzes the first of the sequential glycosyltransferase reactions required for synthesis of the chondroitin sulfate-protein linkage region and formation of polysaccharide chains. It is postulated that xylosyltransferase controls the initiation of chondroitin sulfate chains on core protein. The level of xylosyltransferase in tissue appears to be correlated with amounts of the mucopolysaccharide synthesized.