Multidisciplinary approach to study the effect of water status and mobility on the activity of peroxidase in solutions.

The effect of water mobility on horseradish peroxidase activity in solutions was investigated with a multidisciplinary approach by measuring water activity (aw), freezable water content, 1H proton transverse relaxation time and water self-diffusivity determined by nuclear magnetic resonance. The effect of system mobility as described by viscosity and glass transition temperature (T’g) was also studied. For this purpose, water mobility of aqueous solutions was modulated using ligands (glucose, sorbitol and trehalose) and viscosity was changed upon the addition of maltodextrin. In solutions characterized by different compositions, the effectiveness of a solute in the inhibition of HRP activity is not strictly related to its water mobility depleting effect but depends on the ability of the solute to reduce the overall mobility of the system as described by the inverse of viscosity and T-T’g. The inverse relationship among system viscosity and peroxidase activity was not influenced by the molecular weight of substrate but by the molecular weight of enzyme. Bovine lactoperoxidase (LPO) activity was tested in the same model systems used to test HRP activity and was hindered by viscosity changes more than the latter due to its higher molecular weight.