Altered glutathione S-transferase catalytic activities in female brown bullheads from a contaminated central Florida lake

Brown bullheads (Ameriurus nebulosus) are a demersal freshwater species that can be found in a number of polluted ecosystems. The purpose of the present study was to determine the overall capacity for in vitro glutathione S-transferase (GST) detoxification by brown bullheads, and to see if bullhead GST catalysis was altered in bullheads from a polluted site. Brown bullhead liver cytosolic GSTs catalyzed the conjugation of 1-chloro-2,4-dinitrobenzene (CDNB) over a large range of substrate concentrations, with apparent Km and Vmax for CDNB at fixed nucleophile (glutathione, GSH) concentrations of 1.8–1.9 mM and 12.1–14.6 μmol CDNB conjugated/min/mg, respectively. Bullhead GSTs were also highly active toward other substrates such as ethacrynic acid (ECA), Δ5-androstene-3,17-dione (ADI), and nitrobutyl chloride (NBC). Initial rate GST catalytic activities toward CDNB, NBC, ECA, and ADI were significantly lower in female bullheads from a contaminated lake (Lake Apopka Marsh) as compared to female bullheads inhabiting a nearby control site (Lake Woodruff). No site differences were observed with respect to male bullhead GST activities. These studies suggest that brown bullheads efficiently carry out GST conjugation of diverse electrophilic substrates. However, bullhead GST catalysis may be compromised in bullheads inhabiting polluted ecosystems.