What is the Difference Between Catalase and Peroxidase?

Catalase and peroxidase are both heme enzymes that catalyze reactions involving hydrogen peroxide. However, they have distinct functions and mechanisms:

• Catalase: This enzyme catalyzes the disproportionation of hydrogen peroxide, converting it into water and oxygen. The reaction is as follows: $$2H{2}O{2} \rightarrow 2H{2}O + O{2}$$. Catalase generates a high-valent iron intermediate named Compound I, which oxidizes a second hydrogen peroxide molecule to oxygen.
• Peroxidase: This enzyme uses hydrogen peroxide to oxidize a wide variety of organic and inorganic substrates. The reaction catalyzed by peroxidase is as follows: $$H{2}O{2} + AH{2} \rightarrow 2H{2}O + A$$. Unlike catalase, peroxidase uses Compound I to oxidize other substrates rather than hydrogen peroxide itself.

The difference in reactivity between peroxidases and catalases is likely related to structural differences between the two heme active sites. The nature of the fifth ligand (histidine in peroxidase and tyrosine in catalase) has little effect on the reaction barriers, but the distance between the O(Fe) and O(peroxide) in Compound I significantly affects the reaction barriers. The distal side architecture of peroxidases may not allow for short O(Cpd I)-O(peroxide) distances, resulting in lower efficiency towards hydrogen peroxide oxidation.

Comparative Table: Catalase vs Peroxidase

Catalase and peroxidase are both heme enzymes that catalyze reactions involving hydrogen peroxide, but they have different functions and substracts. Here is a table summarizing their differences:

Catalase is found in nearly all living organisms exposed to oxygen and is crucial for protecting the body from oxidative damage caused by reactive hydrogen peroxide. In contrast, peroxidase can catalyze the decomposition of peroxides, and its optimum substrate is hydrogen peroxide. Some examples of peroxidases include horseradish cytochrome c peroxidase, glutathione peroxidase, and myeloperoxidase.