myrosinase

Myrosinase is an enzyme that catalyzes the hydrolysis of glucosinolates, sulfur-containing secondary metabolites found mainly in plants of the order Brassicales (for example, mustards, horseradish, broccoli, and other cruciferous vegetables). In plants it is usually referred to as a thioglucoside glucohydrolase (EC 3.2.1.147).

Glucosinolates are stored separately from myrosinase in specialized plant tissues. When tissue is damaged, e.g., by chewing or crushing, glucosinolates come into contact with myrosinase, triggering hydrolysis to glucose and an unstable thiohydroxylated aglycone that rearranges to biologically active products such as isothiocyanates, nitriles, or thiocyanates. The outcome is influenced by pH, metal ions, and specifier proteins like epithiospecifier protein (ESP) or nitrile-specifier proteins, which bias the reaction toward isothiocyanates or nitriles.

Isothiocyanates, including sulforaphane, are among the characteristic defense and signaling compounds derived from glucosinolates and contribute to the pungent taste of wasabi and horseradish. In plants, hydrolysis products deter herbivores and pathogens and play a role in signaling within defense pathways.

Genetically, myrosinase activity is carried by several genes, notably TGG1 and TGG2 in Arabidopsis thaliana, which encode canonical myrosinases. Myrosinase activities are also present in various gut microorganisms, and activity can be affected by cooking or processing, which may diminish plant enzyme activity and shift hydrolysis to microbial pathways in the gut.

Industrial and nutritional relevance stems from glucosinolate-derived compounds being studied for cancer chemoprevention and agriculture; processing methods can modulate the release and type of hydrolysis products, affecting flavor, aroma, and health-related properties.