Fetal cartilage xylosyltransferase activity and skeletal growth in sheep

The activity of UDP-D-xylose:proteoglycan core protein beta-D-xylosyltransferase (EC 2.4.2.26), the enzyme that catalyzes the initiation of the polysaccharide chain linkage to the core protein of proteoglycans, was measured in costal cartilage from 20 fetal sheep of 65-138 days gestation. Activity of the enzyme was estimated from the transfer of [14C]xylose from UDP-[14C]xylose to silk as the acceptor protein. The specific activity decreased approximately 10-fold and was found to be highly correlated with the decremental rate of growth in length of the fetal vertebral column. These observations, together with the known gestational decrease in the in vitro rate of uptake of radiolabeled sulfate by ovine fetal cartilage, a subsequent step in proteoglycan synthesis, support the hypothesis that normal fetal skeletal growth is dependent during the last one-half of gestation on the activity of xylosyltransferase in cartilage.