Soluble proteins of liver nuclei of rats fed 3'-methyl-4-dimethylaminoazobenzene

Abstract

Nuclei from livers of rats fed semisynthetic diets with and without 3'-methyl-4-dimethylaminoazobenzene were prepared in 2.1 M sucrose supplemented with magnesium. Approximately 50 per cent of the nuclear nitrogen and 84 per cent of bound azo dyes were soluble in hypotonic Tris-chloride buffer containing magnesium. Magnesiumstabilized nuclear extracts differed in column zonal electrophoresis from the unstabilized saline-phosphate extracts studied previously. The stabilized extracts had substantially more of highly acidic and basic and less of weakly acidic and near-neutral proteins. Furthermore, in the magnesium-stabilized extracts bound azo dyes were predominantly in the highly acidic classes of components and not in near-neutral classes as in the unstabilized saline-phosphate extracts. These and previous studies indicate that in the liver nuclei of rats fed carcinogenic azo dye some protein-azo dye conjugates are free in solution, but some are in magnesium-dependent association with nuclear ribosomes and some are integral parts of nuclear ribosomes.