EFFECT OF DENATURANTS AND STABILIZERS ON PROTEIN ADSORPTION AT SOLID-LIQUID INTERFACES

The adsorption isotherms of different proteins from aqueous solution t o the surface of different solids have been compared in the presence o f additives such as urea, surfactants and high concentration of variou s neutral salts. The adsorption isotherms of lysozyme on alumina are n ot affected much in the presence of 8 M urea showing the rigid structu re. of lysozyme whereas isotherms of hemoglobin show surface coagulati on even in presence of 2 M urea. In presence of 8 M urea, adsorption i sotherms of BSA on alumina show two distinct steps. The extent of prot ein adsorption in the presence of surfactants depends on the nature of surfactants as well as of the underlying surface. The adsorption isot herms of BSA and lysozyme in presence of 2 M concentration of differen t neutral salts have also been compared with each other. In the presen ce of denaturants such as Nal and LICl, the proteins are adsorbed in u nfolded beta-conformation whereas in the presence of protein stabilize rs such as NaCl, KCl and Na2SO2, amount of protein adsorbed at saturat ion is zero or extremely small showing that unfolding of proteins at t he interface is necessary for initial stage of protein adsorption. The standard free energy change (Delta G degrees) per square meter of the surface, signifying relative affinity of a adsorption at the state of monolayer saturation, have been calculated. The magnitude of standard free energy of transfer (Delta G degrees) of one mole of protein to t he surface in presence of all the additives was found close to 40 kJ/m ole.