Uridine diphosphate xylosyltransferase activity in cartilage from manganese-deficient chicks

Abstract

The glycosaminoglycan content of cartilage is decreased in manganese deficiency in the chick (perosis). The activity of xylosyltransferase, the first enzyme in the biosynthetic pathway of sulphated glycosaminoglycans, was studied in the epiphysial cartilage of 4-week-old chicks which had been maintained since hatching on a manganese-deficient diet. Enzymic activity was measured by the incorporation of [14C]xylose from UDP-[14C]xylose into trichloroacetic acid precipitates. Optimal conditions for the xylosyltransferase assay were established and shown to be the same for both control and manganese-deficient cartilage. Assay of the enzyme by using an exogenous xylose acceptor showed no difference in xylosyltransferase activity between control and manganese-deficient tissue. Further, the extent of xylose incorporation was greater in manganese-deficient than in control cartilage preparations, suggesting an increase in xylose-acceptor sites on the endogenous acceptor protein in the deficient cartilage. 35S turnover in the manganese-deficient cartilage was also increased. The data suggest that the decreased glycosaminoglycan content in manganese-deficient cartilage is due to decreased xylosylation of the acceptor protein plus increased degradation of glycosaminoglycan.

Alteration of Cartilage Glycosaminoglycan Protein Acceptor by Somatomedin and Cortisol

“…The medium was changed every 48 hr. Five rudiments were removed at each time point during the incubation and the radioactivity of the 35S relative to uronic acid was determined as described by McNatt et al (13). Figure 2 demonstrates that a medium containing 6.5% of a artially purified serum factor designated somatomedin stimulates 'S incornration into chick ~elvic rudiments.…”