PMC

Distribution of GAGs in the animal kingdom.

The backbone structure of GAGs. CS or DS is composed of alternating disaccharide units of GlcA or IdoA and GalNAc, respectively. R₁, R₂, R₃, R₄ = −H or −SO₃H. Modification with β-D-glucose at the R₂ position has been found in squid CS. The presence of the α-L-fucose branch at the R₄ position has been reported in the CS preparations from sea cucumber and king crab. HS is composed of alternating disaccharide units of GlcA or IdoA and GlcN. R₁ = −COCH₃ or −SO₃H; R₂, R₃, R₄, R₅ = −H or −SO₃H. Recently, sulfation at the R₅ position was discovered in a bivalve HS. HA is a linear polymer composed of GlcA and GlcNAc.