The carbohydrate-protein-binding region in proteokeratan sulfate from bovine cornea is not sulfated.

Peptidokeratan sulfate from bovine cornea was degraded without prior desulfation by hydrazinolysis and nitrous acid deamination and the products were reduced and labelled with NaB3H4. The chain disaccharide units gave, as expected, galactosyl-2,5-anhydromannitol disaccharides with no, one and two sulfate groups, respectively. Desulfation during the degradation procedure was less than 25%. The fraction of the degradation products containing the binding region was identified by its mannose content and size, further separated by mannose-specific affinity chromatography and high-voltage electrophoresis and analysed. 94% of its mannose was found in uncharged oligosaccharides. This indicates that the binding region oligosaccharide bears no sulfate groups.