The horseradish smile: Demonstrating characteristic reactions of peroxidase in a visually appealing way.

Easy and visually appealing demonstrations are precious tools for introducing students to the study of enzymes. However, they most often involve purified enzymes and dedicated techniques. Here, we propose a set of demonstrations, which require only fresh horseradish root and consumer chemicals, to help support biochemistry and enzymology courses from high school to the undergraduate level. Horseradish root is a naturally rich source of horseradish peroxidase, an enzyme with many relevant practical applications. Slices of horseradish root are used to demonstrate the characteristic reaction of horseradish peroxidase with hydrogen peroxide, the selective inhibition of this enzyme by dilute hydrochloric acid, its chromogenic reaction with N,N'-diethyl-p-phenylenediamine, and its ability to trigger the chemiluminescent reaction of luminol. © 2019 International Union of Biochemistry and Molecular Biology, 48(1):38-43, 2020.