The structure of keratan sulphates from various sources

Quantitative structural comparisons were made between keratan sulphates isolated from various sources, namely pig nucleus pulposus, bovine cornea, and the costal cartilages of children, a young adult with Marfan syndrome and of old human autopsies. In human costal cartilage the amount of keratan sulphate increases markedly with age, although total mucopolysaccharide decreases to some extent, concomitant with a decrease in chondroitin 4-sulphate and an increase in chondroitin 6-sulphate. Comparison of molecular weights estimated by gel chromatography with those calculated from the molar ratio of galactose to mannose indicates that keratan sulphates of human costal cartilages of children and of a young adult with Marfan syndrome, and of pig nucleus pulposus, contain one mannose residue per chain, whereas keratan sulphates of old human costal cartilage and of bovine cornea contain one to two, and two, per chain respectively. After mild acid-catalysed desulphation of pig nucleus pulposus keratan sulphate, approx. 12% of the mucopolysaccharide aggregates irreversibly once the water is removed from the polysaccharide. The following conclusions have been drawn from a methylation analysis of keratan sulphates of various sources, aided by g.l.c.-mass spectrometry. (1) Fucose and N-acetylneuraminic acid are non-reducing terminal residues and the sialic acid is linked to the 3-position of galactose residues. (2) Pig nucleus pulposus keratan sulphate has approximately 4 non-reducing terminal groups per molecule and appears to be slightly less branched than the costal-cartilage keratan sulphate of children. The branching in human costal-cartilage keratan sulphates decreases with age. Bovine corneal keratan sulphate appears to be unbranched. (3) Mannose residues are linked by 3 different substituents in human costal-cartilage and bovine corneal keratan sulphates, and by two different substituents in pig nucleus pulposus keratan sulphate. (4) The sulphate ester groups are all on the 6-position of N-acetyl-glucosamine and galactose residues. The degree of sulphation increases with age in costal keratan sulphates with the increase mainly of the galactose 6-sulphate residues.