Alteration of Activation Energy of a Reaction in the Catalase of Human Erythrocyte by Cimetidine, an In vitro Thermokinetic Study

Abstract

Hydrogen peroxide is normally formed during the metabolic pathway of the body. It is a toxic compound for vital cells, which can oxidize many macromolecules and cause damage in cells. Catalase can degrade H2O2 in cells and prevent cell injury. Cimetidine is a histamine H2 receptor blocker which decreases the release of stomach acid and is used for gastrointestinal diseases. Cimetidine inhibited catalase by mixed inhibition. In this study, the effect of temperature on the binding of cimetidine to human erythrocyte catalase was investigated and kinetic factors of the binding were determined. Dixon plot confirmed the mixed type of inhibition and determined the Ki of the drug. The maximum activity of the enzyme was observed at 30°C. Arrhenius plot demonstrated that the activation energy of the enzyme reaction in the absence and presence of cimetidine was about 4.7 and 8.13 kJ/mol, respectively. The temperature coefficient (Q30-40) was determined as about 1.11 and 1.09 in the absence and presence of cimetidine. Cimetidine was able to increase the activation energy of the reaction of catalase, which confirmed the inhibition of the enzyme based on the kinetic results.