During oxidative phosphorylation (where electrons are converted into ATP for the cell by the mitochondria), a certain amount of hydrogen peroxide is formed (H202). This H202 is scavenged by catalase, a protein that catalyzes the dismutation of hydrogen peroxide into water and molecular oxygen as follows: catalase H202 + H202 ------------> 2 H20 + 02.
Catalase is a very strong enzyme, being in an elite group of enzymes which are "kinetically perfect." Kinetic perfection is when the catalytic velocity of the enzyme is restricted only by the rate at which it encounters substrate. In other words, bring it on! as much as you can throw at me and as fast as you can throw it, I can take it! Regarding catalase and pH, I have copied the following posting: "Enzymes typically function over limited range of pH. In the case of catalase, the optimum pH is approximately pH 7.0. That is, catalase works best at a neutral pH. If the solution is too acidic (low pH value) or too basic (high pH value) the catalase is inactive and no longer functions as an enzyme. When you add the sulfuric acid to your catalase reactions you lower the pH below the range where catalase is functional, and the reaction - at least the part catalyzed by catalase - stops. pH affects proteins by changing the state of dissociable amino acid side chains, especially aspartic acid, glutamic acid, lysine, arginine, and histidine. Other groups, such as threonine, serine, and tyrosine, may also be affected at very high pH values. The change in charge on these groups can directly affect catalysis (enzyme activity) if the groups are actually involved in binding the substrate or in the catalytic site of the enzyme. Alternatively, the change in charge of one or more sidechains many lead to a structural change in the protein - i.e. how the protein is folded, or subunits interact, again abolishing activity."