Fluorescence study of Cu2+-induced interaction between albumin and anionicpolyelectrolytes

The Cu2+-induced complex formation of bovine serum albumin (BSA) with anion ic polyelectrolytes (PEs) (polyacrylic acid (PAA), poly(N-isopropylacrylami de) [poly[NIPAAm]], and copolymers of N-isopropylacrylamide (NIPAAm) and ac rylic acid) in aqueous solution was studied by a fluorescence technique and high-performance liquid chromatography analysis. The character of the inte ractions depends on the monomer composition(r = [COOH]/[NIPAAm]), [Cu2+]/[P E], and [BSA]/[PE] ratios and solution pH. Two types of ternary polycomplex (polymer + Cu2+ + BSA) particles are formed depending on the monomer compo sition r of the copolymer. At r from 1/3 to 1/1, the protein molecules in t he structure of ternary polycomplex particles are densely covered by the sh ell of a polymer coil and practically "fenced off' from the water environme nt. At r greater than or equal to 3/1 ternary polycomplex PAA-Cu2+-BSA part icles have more friable structures in which protein molecules are practical ly exposed to the solution. At low polymer concentration, an intrapolymer t ernary polycomplex is formed. This complex aggregates to an interpolymer sp ecies upon increase in polymer concentration. Fluorescence data indicate th at in ternary complex polymer interacts through Cu2+ ions with BSA preferen tially at the site close to the location of "cleft" tryptophan residue. Thi s leads to static quenching of this tryptophan fluorescence. Cu2+-induced c omplex formation is an equilibrium reaction.