Kinetic Parameters of Choline Esterase-Catalyzed Hydrolysis in the Presence of the Antigen-Antibody Immune Complex

The influence of antigen-antibody immune complexes (with the immune pairs of Candida albicans and Phytophtora infestans antigens and the corresponding antibodies) on the catalytic activity of immobilized choline esterase in the enzyme immunosensor was studied. The antigen-antibody immune complex can act as effector of choline esterase, suppressing or enhancing its catalytic activity depending on the ratio of the components of the biospecific interaction (antibodies, antigen, enzyme, and substrate). The kinetic parameters of hydrolysis of butyryl thiocholine iodide, a specific substrate of choline esterase (apparent Michaelis constants, maximal reaction rates, activation and inhibition constants) were calculated at various concentrations of the substrate and antigen and at various dilutions of the antibodies. The types and kinds of the observed effects were determined. The effect of pH on the kinetic parameters of the enzymatic reaction was studied. Various pathways, depending on conditions, were suggested for choline esterase-catalyzed hydrolysis of butyryl thiocholine iodide in the presence of the antigen-antibody immune complex.