Separation of lacquer polysaccharides and interaction with poly-l-lysine

A naturally occurring acidic lacquer polysaccharide with glucuronic acid at the terminals of the complex branches has specific biological activities including promotion of blood coagulation and antitumor activities. The polysaccharide has two molecular weight fractions M¯n=10×104 and M¯n=3.0×104. In the present work, two pure fractions were isolated for the first time by Sephadex G-100 column chromatography. Then, each fraction was treated with diluted alkaline solution to decrease the molecular weights to M¯n=3.0×104 and M¯n=1.4×104, respectively. The NMR and IR spectra and specific rotations of the fractionated and original lacquer polysaccharides were almost identical, suggesting that the lacquer polysaccharides are an associated structure with several low molecular weight polysaccharides of M¯n=1.4×104. Interactions between each lacquer polysaccharide and poly-l-lysine, a model compound of proteins and peptides with positively-charged amino groups, were investigated by surface plasmon resonance (SPR) to elucidate the biological mechanism. The apparent dissociation-rate (kd), association-rate (ka), and dissociation constant (KD) obtained by SPR indicate that the lacquer polysaccharides had weaker interactions with poly-l-lysine than sulfated polysaccharides and that the interaction depended on the molecular weight. These SPR results suggest that the specific biological activities of lacquer polysaccharides originate from electrostatic interaction.