Activity of enzymes immobilized in colloidal spherical polyelectrolyte brushes

We investigate the enzymatic activity of glucoamylase and beta-glucosidase adsorbed on a novel type of colloidal particles. The particles used consist of a poly(styrene) core onto which long chains of poly(acrylic acid) or of poly(styrene sulfonic acid) are grafted ("spherical polyelectrolyte brush"). Proteins adsorb spontaneously onto these particles from aqueous solutions if the ionic strength is low. Moreover, the colloidal stability is not impeded by the adsorbed proteins despite the fact that up to 600 mg of enzyme is adsorbed per gram of the carrier particles. The activity of immobilized glucoamylase and beta-glucosidase adsorbed onto these particles is analyzed in terms of the Michaelis-Menten parameters. This analysis shows that both enzymes keep nearly their full activity. The Michaelis constant K(M) differs only slightly from the K(M) value of the native enzyme when the amount of adsorbed enzyme is raised despite the high local concentration of immobilized enzymes. All data demonstrate that spherical polyelectrolyte brushes present a novel way to immobilize enzymes.