Interaction between chondroitin‐6‐sulfate and poly‐L‐arginine in aqueous solution

The interactions between chondroitin‐6‐sulfate and poly‐ L ‐arginine in aqueous salt solution have been investigated by circular dichroism techniques. In the presence of chondroitin‐6‐sulfate, at neutral pH, poly‐ L ‐arginine adopts the α‐helical conformation rather than “charged coil” form observed in the absence of mucopolysaccharide. This interaction is at a maximum when the ratio of arginine to disaccharide residues is 2:1. Elevation of the temperature leads to a sharp melting transition at 76.0 ± 1.0°C. This behavior is in marked contrast to that for poly‐ L ‐lysine‐chondroitin‐6‐sulfate interactions, which are at a maximum at a 1:1 residue ratio and have a melting transition at 47.0 ± 1.0°C. These results indicate a stronger interaction for poly‐ L ‐arginine than for poly‐ L ‐lysine. The positive arginine side chains appear to interact with both the negative sulfate and carboxyl residues, while those of the lysines are involved only with the sulfates. Poly‐ L ‐ornithine at neutral pH shows no conformation directing interaction with chondroitin‐6‐sulfate, although a small proportion of α‐helix is formed on dilution of the mixture with methanol. The extent of the interaction of cationic polypeptides with chondroitin‐6‐sulfate increases in the order poly‐ L ‐ornithine, poly‐ L ‐lysine, poly‐ L ‐arginine, i.e., in the order of increasing side‐chain length.