Differential expression of alpha-like glutathione S-transferase (GST) isoforms in catfish intestine.

Previous studies suggested that dietary composition affected glutathione S-transferase (GST) activity in catfish intestine, and this activity varied along the intestine. In this study, catfish were fed a semi-purified diet or a commercial chow for at least 2 weeks. GST activity, percent protein cross-reacting with anti-catfish GST pi antibody, and immuno-cross-reactivity with antibodies specific for human alpha, mu, pi and theta class GSTs were determined in cytosol prepared from sections of proximal, medial, and distal intestine. The bulk of GST activity with 1-chloro-2,4-dinitrobenzene (CDNB) and ethacrynic acid, and the percent protein cross-reacting with anti-catfish GST pi were in the more proximal segments and dropped off distally in the two diet groups. The percent of cross-reacting GST protein in the proximal section of fish fed on commercial chow was significantly higher (4.3 +/- 1.7%) than in fish fed purified diet (2.3 +/- 0.2%). Further Western blot analysis revealed a differential expression of GST isoforms only in the distal segment of fish fed commercial chow that recognized human anti-alpha GST antibody. Distal intestinal segments of catfish exposed to 3,3',4,4'-tetrachlorobiphenyl (TCB) and beta-naphthoflavone (BNF) also revealed expression of distinct alpha-like GST isoforms. Results strongly suggest the distal segment as a site for potential biomarkers for polycyclic aromatic hydrocarbon (PAH)- and co-planar polychlorinated biphenyl (PCB)-type contaminants.