SULFATE RELEASE FROM KERATAN SULFATE AND HEPARAN-SULFATE BY BOVINE N-ACETYLGLUCOSAMINE-6-SULFATE SULFATASE

The functions of sulphated monosaccharides within glycosaminoglycans ( GAGs) and glycoproteins are being studied intensely, but progress is h indered by an inability to selectively desulphate glycoconjugates. We recently identified an N-acetylgIucosamine-6-sulphate sulphatase (NG6S S) from bovine kidney that can remove sulphate from N-acetylglucosamin e-6-sulphate (GlcNAc-6-SO4) within oligosaccharides and glycoproteins. However, the potential 'endosulphatase' activity of the NG6SS toward GAGs is not known. To test for this possibility, [H-3]glucosamine-, [H -3]galactose- and (SO4)-S-35-labelled keratan sulphate (KS) were separ ately prepared by metabolic radiolabelling of bovine cornea, NG6SS qua ntitatively removed sulphate from KS without release of sugar fragment s, The enzyme had a K-m of 4.7 mM toward free GlcNAc-6-SO4, but its K- m for commercially available bovine corneal KS was found to be 9.1 mu M. Analyses of both KS and heparan sulphate after treatment with NG6SS demonstrated significant loss of sulphate from GlcNAc-6-SO4 in both G AGs. These findings may be relevant for future studies aimed at defini ng the function(s) of GlcNAc-6-SO4 residues in GAGs and understanding the catabolism of GAGs, especially in regard to sulphatidoses, such as San-filippo D syndrome in humans, which involves a deficiency of NG6S S activity.