Antibodies against rat liver h proteins and against a similar charge class of azoproteins have been labeled with fluorescein isothiocyanate (FITC), and the labeled antisera have been used as histoserological stains on unfixed frozen sections of rat liver. Fixation of antibody was defined by fluorescence microscopy and was used to determine the intracellular distribution of the appropriate antigens. FITC-labeled anti-h protein stained the cytoplasm of both normal and 3′-methyl-4-dimethylaminoazobenzene (3′MeDAB)-treated rat livers uniformly but did not stain 3′MeDAB-induced rat hepatomas. On the other hand, fixation of FITC-labeled antiazoprotein by normal rat liver was concentrated mainly at the periphery of the cell, in the perinuclear region (“membrane” fluorescence) and, to a lesser extent, in the cell cytoplasm. Pretreatment of sections of normal rat liver with unlabeled anti-h protein followed by FITC-labeled antiazoprotein inhibited only the cytoplasmic fluorescence, whereas pretreatment with unlabeled antiazoprotein inhibited both cytoplasmic and “membrane” fluorescence. In sections of liver from 3′MeDAB-treated rats, FITC-labeled antiazoprotein stained only the cytoplasm. This cytoplasmic fluorescence was inhibited by pretreating the sections with unlabeled antiazoprotein but not with unlabeled anti-h protein. The findings have demonstrated that, following administration of 3′MeDAB to rats, there is an alteration in the intracellular distribution of certain liver proteins from a particularly high concentration in the region of the nuclear and plasma membranes to a more uniform dispersal throughout the cell cytoplasm.

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This work was supported by grants from the Australian Tobacco Research Foundation and from the National Health and Medical Research Council of Australia.

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