Relationship between azo dye structure and rat hepatic azoreductase activity

The rate of reduction was determined for a variety of azo dyes using the rat hepatic azoreductase enzyme system. In decreasing order, the rates of reduction for the azo dyes expressed as nmol of arylamine product formed/min/0.25 g of liver were amaranth (33.2), azosulfamide (32.5), orange G (12.4), 1,2-dimethyl-4-p-(carboxyphenylazo)-5-hydroxybenzene (CPA) (9.27), brilliant crystal scarlet (8.00), sulfachrysoidine (7.27), and Sudan I (1.03). A comparison of the partition coefficient with its rate of reduction indicated that the water-soluble azo dyes were reduced more rapidly than the lipid-soluble ones. Furthermore, higher rates of reduction were observed for those dyes containing electron-withdrawing groups on the aromatic rings.