Light Scattering Studies of the Binding of Bovine Serum Albumin to a Cationic

Pol~v(dimethyldiul1ylammonii~m chloride) (PDMDAAC) exhibits u strong electrmtatic in-teraction with bovine serum albumin (BSA) at pH 8.0 in 0.16M NaCl. Electrophoretic. dy-namic, und static light scuttering suggest that the mode of binding of BSA to PDMDAAC de-pends upon the weight concentration ratio (r) qf BSA to PDMDAAC. When r is smaller than cu. 10, the system exhibits characteristics ofcooperative binding, in that the BSA molecules are inhomogmw)uslji distributed among the polymer chains, and free PDMDAAC molecules coex-ist with complex. When r reaches cu. 10. the amount of free PDMDAAC is too small to be observed. Further increase in r leads to a secondary binding process along with an increase in the umoiint qffiee protein. Hydrophobic interactions among the bound BSA are proposed as the driving,fi)rce,fbr the cooperative binding. 0 1996 John Wiley & Sons, Inc