Flexibility, conformational, iduronic acid

Just as the primary structure of heparin and heparan sulfate has a wealth of fine detail, depending on its exact provenance and function, so the exact conformation of a stretch of polysaccharide depends on its exact location in the chain. The key to this conformational flexibility lies in iduronic acid residues, which can adopt either the C4 or the conformation (the glucosamine-derived residues are firmly in the C conformation, as are glucuronic acid residues). Interpretation of vicinal proton proton coupling constants of IdoA residues in terms of an equilibrium between just and conformations suggests the equilibrium changes from 60 40 for internal IdoA residues to 40 60 for terminal residues (Figure 4.84(a)). " ... 

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