Mannose in the keratan sulfate from bovine cornea

After exhaustive digestion of bovine corneas with a protease, keratan sulfate fractions of different chain length were obtained by ethanol fractionation on a cellulose column, followed by ion-exchange column chromatography. Compositional analysis of these fractions showed that aspartic acid is the predominant amino acid and that the keratan sulfate in each fraction contains aspartic acid and mannose in the molar ratio of 1:3. Molecular weights of these fractions, estimated by gel chromatography, were close to the calculated values based on the molar ratios of the components to three moles of mannose. The results strongly suggested that the keratan sulfate of bovine cornea contains three mannose residues per chain, as an integral component of the linkage region to protein.