Structural Analysis of Unsaturated Hexasaccharides Isolated from Shark Cartilage Chondroitin Sulfate D that are Substrates for the Exolytic Action of Chondroitin ABC Lyase

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Abstract
The enzymatic action of highly purified chondroitin ABC lyase from Proteus vulgaris is dependent on the size of the substrate, and the enzyme does not cleave tetrasaccharides, irrespective of their sulfation profiles [Sugahara, K., Shigeno, K., Masuda, M., Fujii, N., Kurosaka, A. & Takeda, K. (1994) Carbohydr: Res. 255, 145–163]. To characterize the enzyme action in more detail, we isolated nine sulfated hexasaccharides from commercial shark cartilage chondroitin sulfate D, after partial digestion with highly purified chondroitin ABC lyase, by means of gel chromatography and HPLC on an amine‐bound silica column. Structural analysis by 500‐MHz 1H‐NMR spectroscopy, and enzymatic digestion in conjunction with HPLC, demonstrated that these hexasaccharides, with the common core saccharide structure ?4HexA(α1‐3)‐GalNAc(βl‐4)GlcA(β1‐3)GalNAc(β1‐4)GlcA(β1‐3)GalNAc (where ?4HexA and GlcA represent 4‐deoxy‐α‐l‐threa‐hex‐4‐enepyranosyluronic acid and glucuronic acid, respectively) bear three or four sulfate groups in different combinations. In the hexasaccharides, the D disaccharide unit GlcA2‐SO3−(β1‐3)GalNAc6SO3−, which is characteristic of chondroitin sulfate D, was arranged on the reducing side of the A disaccharide unit GlcA(βl‐3)GalNAc4SO3−, and thus formed an A‐D tetrasaccharide sequence GIcA(β1‐3)GalNAc4SO3−(β1‐4)GlcA2SO–(β1‐3)GalNAc6SO3−. Analysis of the degradation products of these hexasaccharides with highly purified chondroitin ABC lyase indicated that the enzyme preferentially acted on the unsaturated hexasaccharides in an exolytic fashion and removed an unsaturated disaccharide unit from the non‐reducing termini, irrespective of the sulfation profiles of the hexasaccharides.

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