Glucuronosyl transfer to galactose residues in the biosynthesis of HNK-1 antigens and xylose-containing glycosaminoglycans: one or two transferases?
An early step in the assembly of the xylose----serine-linked proteoglycans is the transfer of glucuronic acid to the C-3 position of a galactose residue in the carbohydrate-protein linkage region. Since a similar reaction occurs in the biosynthesis of NHK-1 antigens, the question arose whether these processes are catalyzed by the same enzyme. In the present study, the proteoglycan-related glucuronosyltransferase activity in embryonic chick brain was found to be firmly membrane-associated, while the majority of the activity towards N-acetyllactosamine - a model substrate for HNK-1 antigen biosynthesis - was readily solubilized. No activity towards N-acetyllactosamine was found in embryonic chick cartilage, which is a rich source of the proteoglycan-related enzyme. Together with the results of mixed substrate experiments, these findings strongly indicate the existence of two separate glucuronosyltransferases catalyzing transfer to galactose residues.
Curenton
T
T
Laboratory of Medical Genetics, University of Alabama, Birmingham 35294.
Ekborg
G
G
Rodén
L
L
D000818:Animals; D000943:Antigens, Differentiation / Q000096:biosynthesis*; D001921:Brain / Q000201:enzymology*; D018959:CD57 Antigens; D002240:Carbohydrate Sequence; D002642:Chick Embryo; D005690:Galactose / Q000378:metabolism*; D014453:Glucuronosyltransferase / Q000378:metabolism*; D006025:Glycosaminoglycans / Q000096:biosynthesis*; D007527:Isoenzymes / Q000378:metabolism*; D008969:Molecular Sequence Data; D012694:Serine; D013347:Subcellular Fractions / Q000201:enzymology; D013379:Substrate Specificity; D014994:Xylose / Q000378:metabolism*
D000943:Antigens, Differentiation; D018959:CD57 Antigens; D006025:Glycosaminoglycans; D007527:Isoenzymes; D012694:Serine; D014994:Xylose; D014453:Glucuronosyltransferase; D005690:Galactose