Catalyzes the reductive cleavage of azo bond in aromatic azo compounds to the corresponding amines. Requires NADPH, but not NADH, as an electron donor for its activity. The enzyme can also reduce a wide range of sulfonated azo dyes. The substrate preference order is methyl red > Ponceau BS, Ponceau S > Orange II > Amaranth. anthranilate + N,N-dimethyl-1,4-phenylenediamine + 2 NAD(+) = 2-(4-dimethylaminophenyl)diazenylbenzoate + 2 H(+) + 2 NADH Optimum pH is 6.0-6.6. Optimum temperature is 35-40 degrees Celsius. Inactive above 60 degrees Celsius. Thermostable up to 55 degrees Celsius. Homotetramer. Constitutively expressed. Belongs to the azoreductase type 2 family.