IDENTIFICATION OF 2 BINDING-PROTEINS FOR HALOGENATED AROMATIC-HYDROCARBONS IN THE HARD-SHELL CLAM, MERCENARIA-MERCENARIA

Earlier studies have reported an unusually high incidence of gonadal t umors in marine bivalves in areas of potentially high exposure to herb icides including 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophe noxyacetic acid. Some herbicides can be contaminated by halogenated ar omatic compounds including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Most of the effects of planar halogenated aromatic compounds, includi ng carcinogenic effects in vertebrates, appear to be mediated through binding to the aryl hydrocarbon receptor. The current study investigat ed whether halogenated aromatic hydrocarbon-binding proteins are prese nt in the marine bivalve, Mercenaria mercenaria. We used the TCDD phot oaffinity analog 2-azido-3-[I-125]-iodo-7,8-dibromodibenzo-p-dioxin to detect the presence of two proteins (28 and 39 kDa) in cytosols prepa red from M. mercenaria that specifically bound this ligand. Expression of these proteins is tissue-dependent with the highest concentrations being observed in gill and gonadal tissue. Gonadal tissue also exhibi ted gender-specific expression with female clams exhibiting higher lev els of the 39-kDa protein. Gender and tissue-specific expression are c onsistent with the hypothesis that these proteins might be involved in the carcinogenic response observed in clams exposed to herbicides. (C ) 1995 Academic Press, Inc.