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Binding of 3'-Methyl-N,N-dimethyl-4-aminoazobenzene Metabolites to Rat Liver Cytosol Proteins and Ligandin Subunits¹

Liver Research Center and Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461

Twenty min after i.p. administration of 3'-[¹⁴C]methyl-N,N-dimethyl-4-aminoazobenzene in corn oil to rats, 0.73% of administered radioactivity was present in the liver. Only 0.45% of radioactivity present in liver was recovered in the nuclear fraction, whereas 25% was present in the cytosol fraction. Twenty-seven % of cytosolic radioactivity was trichloroacetic acid precipitable, and 2% was immunoprecipitable with monospecific anti-rat liver ligandin immunoglobulin G. After 3 hr of administration, 3.2% of administered radioactivity was present in the liver, 40% of which was in the cytosol. Although 59% of radioactivity present in liver cytosol was trichloroacetic acid precipitable as compared to 27% at 20 min, the radioactivity precipitated by anti-ligandin immunoglobulin G was still 2%.

When liver cytosol obtained from rats after 20 min of 3'-[¹⁴C]methyl-N,N-dimethyl-4-aminoazobenzene administration was fractionated on a Sephadex G-75 column, three peaks of radioactivity were observed. When cytosol was subjected to sodium dodecyl sulfate gel electrophoresis and fluorography, radioactivity was mainly associated with 5 proteins with molecular weights of 88,000, 47,000, 41,000, 31,000, and 22,000. When the immunoprecipitate obtained from cytosol with antiligandin immunoglobulin G was subjected to sodium dodecyl sulfate gel electrophoresis and fluorography, radioactivity was exclusively associated with the subunit of ligandin with a molecular weight of 22,000. Approximately 90% of the radioactivity in the immunoprecipitate was covalently associated with this subunit. These studies reveal that 3'-methyl-N,N-dimethyl-4-aminoazobenzene or its metabolities are selectively bound to the subunit of ligandin with a molecular weight of 22,000 and four other cytosol proteins in vivo.

¹ This work was supported by Grants CA 24842, AM 17702, and 2019 from the NIH.

² To whom requests for reprints should be addressed.

Received 10/ 3/80. Accepted 6/11/81.