Control of chondroitin sulphate biosynthesis. β-d-Xylopyranosides as substrates for UDP-galactose: d-xylose transferase from embryonic-chicken cartilage

Abstract

Embryonic chicken epiphyseal cartilage was incubated in vitro with a variety of .beta.-xylosides and the amount of [3H]acetate incorporation into chondroitin sulfate was determined under conditions when normal protein core production was inhibited by cycloheximide. Ability of the different .beta.-xylosides to relieve the cycloheximide-mediated inhibition of chondroitin sulfate synthesis was influenced by the nature of the aglycan group of the xyloside. .beta.-Xylosides with apolar and uncharged aglycan groups were most effective and produced a several-fold stimulation of chondroitin sulfate biosynthesis. .beta.-Xylosides with charged aglycan groups were less effective initiators of chondroitin sulfate synthesis. The rate of galactose transfer from UDP-galactose to each of the .beta.-xylosides, catalyzed by a cell-free microsomal preparation from embryonic cartilage, was measured. The nature of the aglycan group of the .beta.-xyloside was a factor determining the capacity of the xyloside to act as an acceptor for galactosyltransferase I, the enzyme that catalyzes the first galactose transfer reaction of chondroitin sulfate synthesis. The aglycan group of the xyloside also appeared to influence other steps leading to chondroitin sulfate chain initiation in vitro.