It is very important to clarify the mechanisms of the interaction between components of organisms. In this report, the interaction between bovine serum albumin (BSA) and ionic polysaccharides were discussed.
The fluorescence spectrum of tryptophan (Trp) in BSA changed as its conformation changed. On adding polysaccharide containing sulfonic acid residues (sulfonic-type) at pH 7.4, a remarkable blue shift of the emission maximum (! em ) of Trp was observed. This blue shift was decreased by adding NaCl. In contrast, polysaccharide containing carboxylic acid residues (carboxy-type) scarcely changed Trp fluorescence at the same pH. At a pH lower than the isoelectric point (PI = 4.7ยฑ 4.9) of BSA, a remarkable blue shift was observed not only by adding sulfonic-type polysaccharide but also by adding carboxy-type polysaccharide.
Moreover, using the energy transfer method, in the pH region higher than the PI of BSA, carboxylic-type polysaccharides may interact relatively weakly with the binding site II of BSA, but sulfonic-type ones can selectively interact with binding site I weakly and with binding site II strongly. And in the pH region lower than the PI of BSA, carboxylic-type polysaccharides interact with binding site II strongly. On the other hand, sulfonic-type polysaccharides are bound to both binding site I and binding site II very strongly.