(269e) Enzymatic Hydrolysis of Proteins in Bulk Solutions and at Liquid/Air, Liquid/Solid Interfaces: Effect of Surfactants
Proteases are common components of automatic dishwashing and laundry formulations assisting in the removal of proteinaceous stains. Mechanistic understanding is lacking of adsorption and kinetic behavior of protease/surfactant mixtures in the cleavage of surface-immoblized proteins. We study the kinetics of protein hydrolysis by the serine protease Subtilisin Carlsberg employing fluorescent assay for the bulk aqueous solution, optical waveguide lightmode spectroscopy (OWLS) for protein-stain removal from a solid surface, and flow tensiometry for protein removal from the liquid/air interface. We find that all surfactants studied reduce bulk proteolysis rates due to substrate-screening. However, these same surfactants enhance protein removal from both the solid/water and air/water interfaces. Moreover, the mixed enzyme/surfactant solutions perform better than their single-component counterparts at both the solid/water and air/water interfaces. A simple Langmuir-Michaelis-Menton (LMM) kinetic model is proposed to describe the kinetics of the simultaneous enzyme adsorption and substrate cleavage of the surface-immobilized protein layers. This model well describes the enzymatic-cleavage dynamics of different solid-surface-immobilized protein substrates removal. The LMM model is extended to describe the dynamics of protein-stain removal by protease-surfactant mixtures. We find that surfactant and enzyme compete for the surface-immobilized protein active sites when applied together.