Plasma membranes were prepared from livers of normal and N-2-fluorenylacetamide-ingesting rats. Of the two marker enzymes studied, the activity of 5′-nucleotidase was markedly decreased, whereas that of Mg2+-Na+-K+-ATPase was unaffected in the membranes from animals fed the carcinogen. The percentage of phospholipids in the preneoplastic and neoplastic liver membranes was very much higher than in the controls, and the phospholipid:cholesterol ratio was also significantly enhanced. The percentage of polyunsaturated fatty acids was higher in these membranes than in the plasma membranes of normal liver. Unlike in preparations from normal livers, a large amount of floating fraction (d < 1.16) was invariably observed in membrane preparations from preneoplastic and neoplastic livers.

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Supported by a grant from the American Cancer Society and Grant CA-01932 from the USPHS. A preliminary report has been published (6).

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