Background: 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.
Objective: 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.
Results: 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.
Conclusion: 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.