Kinetic parameters of choline esterase-catalyzed hydrolysis in the presence of the antigen-antibody immune complex

The influence of anti gen-an ti body immune complexes (with the immune pair s of Candida albicans and Phytophtora infestans antigens and the correspond ing antibodies) on the catalytic activity of immobilized choline esterase i n the enzyme immunosensor was studied. The antigen-antibody immune complex can act as effector of choline esterase, suppressing or enhancing its catal ytic activity depending on the ratio of the components of the biospecific i nteraction (antibodies, antigen, enzyme, and substrate). The kinetic parame ters of hydrolysis of butyryl thiocholine iodide, a specific substrate of c holine esterase (apparent Michaelis constants, maximal reaction rates, acti vation and inhibition constants) were calculated at various concentrations of the substrate and antigen and at various dilutions of the antibodies. Th e types and kinds of the observed effects were determined. The effect of pH on the kinetic parameters of the enzymatic reaction was studied. Various p athways, depending on conditions, were suggested for choline esterase-catal yzed hydrolysis of butyryl thiocholine iodide in the presence of the antige n-antibody immune complex.