Modulation of egg-white lysozyme activity by viscosity intensifier additives

The activity of egg-white lysozyme was measured in the presence of carbohydrate additives in the reaction medium. These additives show a significant affinity for water. They depress water activity and increase the viscosity of the medium. Solute-solvent interactions in aqueous solutions of the additives are characterized by properties such as the intrinsic viscosity, Huggins constant apparent molar volume and hydration number. It was found that, despite the lowering of enzyme activity when the concentration of additive is increased, the behavior remains Michaelian and neither modification of Km nor inhibition by excess substrate is observed. On the other hand, the effect of the viscosity of the medium on enzyme activity was determined. This effect is independent of the nature of the additive at high viscosities (greater than 4 mPa s-1) for which enzyme activity is very low and appears to vary according to the kind of additive in dilute solution at low viscosities (less than 2 mPa s-1).