The Influence of Humic Acids on the Activities of Lysozyme and Urease

To evaluate electrostatic interactions between humic acids and proteins and the effects of pH, ionic strength and mass ratios (HAs/enzymes) on activities of immobilized enzymes, soil humic acids (including HA and FA) and two enzymes (lysozyme and urease) were applied in our experiment. Electrostatic attraction and repulsion play important roles in their interaction, which is also pH dependent. Salt could screen not only electrostatic attraction but also repulsive force, which is dependent on the mixing fractions of HAs and enzymes. Two mechanisms were presented for the interaction of HAs with lysozyme and urease: encapsulated lysozyme into humic acid network structure to block the active sites or deformation of the tertiary structure of lysozyme and adsorbed urease onto humic acids to stabilize the enzyme structure.