Ligandin subunits and hepatocellular carcinoma in man and rat.

Covalent binding of activated azo dye and methyl cholanthrene carcinogens preferentially occurs to subunit B of ligandin. This subunit contains 7 of ligandin's 9 cysteine residues which, according to Ketterer et al, are the site of covalent carcinogen binding. Subunit B appears to be cytoplasmic and intranuclear. We postulate that binding of activated carcinogens to subunit B may facilitate their transfer from cytoplasm to nucleus. Rat and human primary liver cell cancers often contain ligandin which is released into the circulation. In patients at risk for, or suspected of having primary liver cell cancer, increased serum ligandin concentrations may have diagnostic value.