The structure and function of enzymes is a central theme in cellular and molecular biology. In this laboratory exercise, a crude cell extract is prepared from potatoes.
Activity of the enzyme, catalase [which catalyzes the reaction 2H2O2(l) → 2H2O(l) + O2(g)], is then studied using a simple assay for O2. To conduct the assay, a filter is soaked in crude potato extract, then transferred to the bottom of a beaker containing hydrogen peroxide. Catalase causes O2 to collect in the filter, which in turn causes the filter to rise. Students are able to explore the effect of enzyme and/or substrate concentration and pH on the amount of product formed by measuring the time taken for each filter to collect enough oxygen to rise. Students average their results, calculate the inverse of the “time to rise,” and pool the data in order to plot the characteristic curve showing the dependence of enzyme activity on substrate and enzyme concentration.