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Pattern of 2-methyl-4-dimethylaminoazobenzene-binding proteins in the livers of partially hepatectomized rats and of continuously dye-fed rats in comparison with 3'-methyl-4-dimethylaminoazobenzene.

Partially hepatectomized and sham-operated rats received 2-methyl-4-dimethylaminoazobenzene (2-Me-DAB) in a single dose (10 mg) and normal rats were fed a diet containing 0.06% 2-Me-DAB for 2-week and 1-month periods. The patterns of dye-binding proteins in the cytosols prepared from the livers of these rats were investigated by chromatography on carboxymethylcellulose as well as by gel filtration in Sephadex G-100, and the results were compared with those of rats given 3′-methyl-4-dimethylaminoazobenzene (3′-Me-DAB) under the same conditions. It was found that 2-Me-DAB given in a single dose is preferentially bound to the slightly basic protein fractions (Fractions IV and VI) in sham-operated rats but to the nonbasic protein fraction (Fraction I) in partially hepatectomized rats, while 3′-Me-DAB is preferentially bound to Fraction I in both cases. Gel filtration of Fraction I revealed that 3′-Me-DAB is preferentially bound to the higher-molecular-weight subomponent (1-a) in both sham-operated and partially heaptectomized rats, while 2-Me-DAB is bound to the smaller-molecular-weight subcomponent (I-b) in the shamoperated rat liver but to I-a in the regenerating liver. For Fraction IV, 3′-Me-DAB is bound to the higher-molecularweight subcomponent (IV-a) in sham-operated rats but to the lower-molecular-weight subcomponents (IV-b, c) in partially hepatectomized rats, while 2-Me-DAB is bound to the lower-molecular-weight subcomponents in both sham-operated and partially hepatectomized rats. The results supported our previous finding that dye binding to I-a target protein may be involved in chemical carcinogenesis.

The pattern of dye-binding proteins does not change during continuous feeding of 2-Me-DAB, which is in contrast to the dramatic change in the dye-binding protein pattern during continuous feeding of 3′-Me-DAB.