azoreductases

Azoreductases are enzymes that catalyze the reductive cleavage of azo bonds (N=N) found in azo dyes and related compounds. In bacteria and some fungi, these enzymes initiate decolorization by transferring electrons from NADH or NADPH to the azo linkage, typically via a flavin cofactor such as FMN or FAD. The reduced azo bond is cleaved to yield two aryl amines, which may then be further metabolized by other cellular enzymes. The reactions commonly occur under anaerobic or reducing conditions, and some azoreductases show activity in microaerobic environments, though oxygen can suppress activity in others.

Most well-characterized azoreductases are flavin-dependent cytosolic enzymes with broad substrate specificity, including many textile dyes such as Orange II and various Direct/Reactive dyes. Substrate scope and product distribution depend on the enzyme and the cofactor providing the electrons (NADH versus NADPH) and on substituents on the aromatic rings. In bacteria, azoreductase genes (often termed azoR or related) are frequently inducible by azo compounds and participate in dye degradation as part of broader catabolic pathways.

Applications include bioremediation and wastewater treatment, where azoreductases contribute to color removal and detoxification of azo dyes. They are also explored as biocatalysts for synthesis or for pathways that convert azo dyes to metabolizable amines; however, the resulting products can be hazardous and require further processing. Ongoing research seeks to expand substrate ranges, improve catalytic efficiency, and integrate azoreductases into environmental and industrial workflows.