Polysaccharide, anionic, binding

In the pH range close to the protein s lEP an interesting phenomenon of non-uniform redistribution of protein molecules among polysaccharide chains occurs (Tolstoguzov et al. 1985). The reason is that in the vicinity of the protein lEP the hydrophobic protein-protein and electrostatic protein-polysaccharide interactions can be energetically comparable with each other. Protein-protein association on the anionic polysaccharide matrix (or self-association of proteins), which is mainly due to hydrophobic interactions, is usually enhanced when the pH approaches the protein lEP. Accordingly, under conditions of a relatively weak protein-polysaccharide interaction, each free site situated near the site on the polysaccharide chain already occupied by a protein molecule becomes thermodynamically preferable for further binding of protein molecules. This leads to cooperative protein adsorption on an anionic polysaccharide. Some parts of polysaccharide chains tend to be completely covered by protein molecules (as in a virus) while other parts are completely free of protein. 

Other molecules have been suggested as being useful lung-specific bioadhesive agents [137,138], for example, insulin, transferrin, prostaglandins, hirudin-inhibited thrombin (which binds thrombomodulin), anionic polysaccharides, oligosaccharides (such as dextran sulfate, dermatan sulfate, chondroitin sulfate, hyaluronic acid), peptides (such as benzoyl-phe-ala-pro [BPAPI] that... 

Malovikova A, Hayakawa K, Kwak JCT. Binding of alkylpyridinium cations by anionic polysaccharides. ACS Symposium Series 1984 253 225-239. 

Alginic acid, also called algin or alginate, is an anionic polysaccharide distributed widely in the cell walls of brown algae. It binds with water to form a viscous gum. It absorbs water quickly and is capable of absorbing 200-300 times of water by its weight [142]. It is biocompatible and less toxic with relatively low cost and forms mild gelation by the addition of cations such as Na+ and Ca + [143]. 

Carboxymethylcellulose, like the majority of anionic polysaccharides, strongly binds certain multivalent cations even small amounts of Ca or other multivalent metal ion... 

The anionic polysaccharides, though structurally diverse, share some common characteristics. Most of those described above interact strongly with multivalent cations calcium ion (Ca ), in particular, binds tightly. This binding can be beneficial, e.g., the gel formation of... 

The addition of cationic surfactant to an anionic polysaccharide solution shows its greatest effect near the surfactant cmc. As the surfactant concentration increases beyond the cmc, the polysaccharide may go back into solution or it may form an insoluble complex, flocculate, and settle out of solution. In general, as the polysaccharide s anionic charge increases, so does its interaction with cationic surfactants. As an example, alginic acid binds more strongly to cationic surfactants than carboxymethylcellulose. 

Several naturally occurring anionic polysaccharides exist alginic acid, pectin, carrageenans, xanthan gum, hyaluronic acidic, gum exudates (gum arabic, karaya, traganth, etc.). Cross-linking sites that occur when a polyvalent cation (e.g. Ca +) causes interpolysaccharide binding are called "junction zones . 

---