COADSORPTION OF IGG AND BSA ONTO SULFONATED POLYSTYRENE LATEX .1. SEQUENTIAL AND COMPETITIVE COADSORPTION ISOTHERMS

In this work the sequential and competitive coadsorption of IgG and BS A proteins on a sulfonate polystyrene latex with high surface charge d ensity have been studied. For sequential coadsorption the IgG/a-CRP wa s first adsorbed and then the free surface of the particle was saturat ed by redispersion of the pellet in a solution with a high concentrati on of monomeric BSA (m-BSA). The competitive coadsorption experiments were carried out in two separate experiments by changing the initial c oncentration of one protein when the concentration of other protein wa s high and constant. During the incubation the pH was 5 or 6, and the ionic strength 2 mM, as in previous studies the adsorption of BSA was very low at neutral or basic pH regardless of the amount of adsorbed I gG. From these coadsorption experiments it was possible to obtain late x-protein complexes with a similar degree of coverage by each protein, high adsorption of IgG and different amounts of BSA, or high adsorpti on of BSA and a low, but significant, amount of IgG. The latex-protein complexes were electrokinetically characterized by measuring the elec trophoretic mobility of each complex vs the pH of redispersion. In tha t way we can detect the i.e.p. of the complexes and the pH range in wh ich the electrostatic repulsion can make them colloidally stable.