Polyacrylamide gels as support for enzyme immobilization by entrapment. Effect of polyelectrolyte carrier, pH and temperature on enzyme action and kinetics parameters

This study investigates the main interactions which occur among enzymes and the polymeric support in which they are immobilized, when charges are created within the support as a result of the effect of external variables. The electrostatic field generated by the charges has a major impact on the enzymatic activity and kinetic parameters. In the most extreme conditions for the external variables, the pH of the interior of the support is displaced by 1.5 pH units towards more alkaline values. Measured at pH 10.0, the Michaelis constant for immobilized enzymes is 17 times higher than for free enzymes. The displacement in the pH-activity profiles, pH of the interior of the support and the kinetic parameters is a consequence of the non-uniform distribution of the hydrogen ions and negatively charged substrate molecules between the microenvironment of the enzyme and that of the solution. The theoretical analysis of the electrostatic potential created by the charges of the support allows obtaining correlations to quantify the displacement of these parameters.