# Can a very high concentration of hydrogen peroxide, inhibit or denature the enzyme catalase?

My experiment, where I am investigating the effect of increasing substrate concentration of hydrogen peroxide on enzyme activity hasn't worked out as I hoped. The last result, highest concentration of hydrogen peroxide, shows a decrease in enzyme activity compared to the lower substrate concentration and I don't understand why?

• We need more details to be able to help you. What specific concentrations of hydrogen peroxide did you try? Nanomolar? Or molar? It makes a big difference in possible explanations for what is happening. – Curt F. Nov 29 '15 at 14:55
• It was 1, 3, 5, 10, 15 and 20% solutions of hydrogen peroxide with 2% catalase. I put 10cm^3 of hydrogen peroxide and 5cm^3 of catalase solution in a measuring cylinder with o.1cm^3 of washing liquid. The volume of bubbles produced corresponds to enzyme activity. Its a pretty basic high school experiment – George Nov 29 '15 at 15:15

20% hydrogen peroxide sounds HUGE. But something can happen that is called substrate inhibition. It can be detected if the substrate acts as a non-competitive reversible inhibitor (i.e. binds only to the active ES Michaelis complex). In the case I studied during my PhD, the inhibition constant ($K_\mathrm{i}$) was roughly 1000 times higher that the Michaelis constant ($K_\mathrm{M}$). The steady-state rate was well fit with : $$r = \frac{r_\infty}{1+\frac{K_\mathrm{M}}{s} + \frac{s}{K_\mathrm{i}}}$$ So the activity would go through a maximum ($s$ is substrate concentration).
Tip : if it is possible, do you assays with substrate concentrations growing exponentially, like $1\,\mathrm{\mu M}$, then 2, 5, 10, 20, etc.