Xylosylation and glucuronosylation reactions in rat liver Golgi apparatus and endoplasmic reticulum

• Published in: The Journal of biological chemistry 1986-10, Vol.261 (28), p.12936-12941
• Main Authors: Nuwayhid, N, Glaser, J H, Johnson, J C, Conrad, H E, Hauser, S C, Hirschberg, C B
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Carbohydrate Conformation; Cell structures and functions; Endoplasmic Reticulum - metabolism; Fundamental and applied biological sciences. Psychology; Galactose - metabolism; Glucuronates - metabolism; Glucuronic Acid; Glucuronosyltransferase - metabolism; Golgi apparatus; Golgi Apparatus - metabolism; Kinetics; Liver - ultrastructure; Molecular and cellular biology; Rats; Uridine Diphosphate Galactose - metabolism; Uridine Diphosphate Xylose - metabolism; Xylose - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)69252-X

We have studied in rat liver the subcellular sites and topography of xylosylation and galactosylation reactions occurring in the biosynthesis of the D-glucuronic acid-galactose-galactose-D-xylose linkage region of proteoglycans and of glucuronosylation reactions involved in both glycosaminoglycan biosynthesis and bile acid and bilirubin conjugation. The specific translocation rate of UDP-xylose into sealed, "right-side-out" vesicles from the Golgi apparatus was 2-5-fold higher than into sealed right-side-out vesicles from the rough endoplasmic reticulum (RER). Using the above vesicle preparations, we only detected endogenous acceptors for xylosylation in the Golgi apparatus-rich fraction. The specific activity of xylosyltransferase (using silk fibroin as exogenous acceptor) was 50-100-fold higher in Golgi apparatus membranes than in those from the RER. Previous studies had shown that UDP-galactose is translocated solely into vesicles from the Golgi apparatus. In these studies, we found the specific activity of galactosyltransferase I to be 40-140-fold higher in membranes from the Golgi apparatus than in those from the RER. The specific translocation rate of UDP-D-glucuronic acid into vesicles from the Golgi apparatus was 10-fold higher than into those from the RER, whereas the specific activity of glucuronosyltransferase (using chondroitin nonasaccharide as exogenous acceptor) was 12-30-fold higher in Golgi apparatus membranes than in those from the RER. Together, the above results strongly suggest that, in rat liver, the biosynthesis of the above-described proteoglycan linkage region occurs in the Golgi apparatus. The specific activity of glucuronosyltransferase, using bile acids and bilirubin as exogenous acceptor, was 10-25-fold higher in RER membranes than those from the Golgi apparatus. This suggests that transport of UDP-D-glucuronic acid into the RER lumen is not required for such reactions.