The isolation and characterization of polycyclic hydrocarbon-binding proteins from mouse liver and skin cytosols

The major protein to which metabolites of methylcholanthrene are covalently bound has been purified from C3H mouse liver cytosol. Its properties are identical to the mouse skin h-protein, which may be primary arget of carcinogenic hydrocarbon metabolites during transformation to caner. It has a molecular wight of 44,000, consists of 2 subunits o- M.W. 20,000, has an isoelectric point (pI) of 8.05 to 8.6, and a sedimentation coefficient of 3.6 S. These physical properties are rather similar to those of ligandin, a hepatic protein that binds carcinogen metabolites, steroid anionic metabolites, bilirubin, and exogenous organic anions, but not to those of the rat liver azo dye carcinogen binding 'slow h-2-5S' protein. The h-protein and ligandin consistently give different pl values. Two minor basic proteins (molecular weights around 44,000 each), to whcih methylcholanthrene metabolites are convalently bound, have been separated from the h-protein by carboxymethyl-cellulose chromatography. Prelininary results indicate that these 2 minor proteins are related to ligandin. A protein to which methylcholanthrene is noncovalently bound was also identified in the acidic fraction of the mouse liver and skin sytosols and has been partially purified and characterized. It has a molecular weight of 60,000, a pl of 5.0, and a sedimentation coefficient of 4.5S.