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The Isolation and Characterization of Polycyclic Hydrocarbon-binding Proteins from Mouse Liver and Skin Cytosols¹

McArdle Laboratory for Cancer Research, The Medical School, University of Wisconsin, Madison, Wisconsin 53706

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 a primary target of carcinogenic hydrocarbon metabolites during transformation to cancer. It has a molecular weight of 44,000, consists of 2 subunits of 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 h₂-5S" protein. The h-protein and ligandin consistently give different pI values. Two minor basic proteins (molecular weights around 44,000 each), to which methylcholanthrene metabolites are covalently bound, have been separated from the h-protein by carboxymethyl-cellulose chromatography. Preliminary 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 cytosols and has been partially purified and characterized. It has a molecular weight of 60,000, a pI of 5.0, and a sedimentation coefficient of 4.5 S.

¹ This work was supported in part by Grant CA-07175 from the National Cancer Institute, NIH, and by Grant BC-2D from the American Cancer Society.

² Present Address: Department of Experimental Therapeutics, Roswell Park Memorial Institute, Buffalo, N. Y. 14203.

³ American Cancer Society Professor of Oncology.

Received 7/ 1/74. Accepted 12/12/74.