Activities of affinity-isolated glutathione S-transferase (GST) from channel catfish whole intestine.

A glutathione S-transferase (GST) fraction was isolated from cytosol prepared from catfish intestinal mucosa by GSH-agarose affinity chromatography and its molecular weight, isoelectric points, substrate specificities and immunochemical cross-reactivity were examined. Intestinal GSTs were purified 100-fold with respect to cytosolic activity with 1-chloro-2, 4-dinitrobenzene and had high activity with ethacrynic acid, (+/-)benzo(a)pyrene-4,5-oxide, and (+/-)anti-benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide, but a low activity with 1,2-dichloro-4-nitrobenzene. SDS-polyacrylamide gel electrophoresis revealed the presence of a single band with relative molecular mass of 26700. Gel isoelectric focusing showed a major band with a pI of 8.2. A polyclonal antibody prepared against a GST pi-protein isolated from catfish proximal intestine cross-reacted well with the affinity isolated GST fraction. The catfish antibody also cross-reacted with GST from human placenta which contains predominantly pi-class GST (Mannervik, B., Guthenberg, C., 1981. Glutathione transferase (human placenta). In: Jakoby, W.B. (Ed.), Methods in Enzymology, 77. Academic Press, New York, pp. 231-235; Polidoro, G., Dillio, C., Arduini, A., Frederici, G., 1981. Molecular and catalytic properties of purified glutathione transferase from human placenta. Biochem. Med. 22, 247-259; Dao, D.D., Partridge, C.A., Kurosky, A., Awasthi, Y.C., 1982. Subunit structure of glutathione-S-transferase of human liver and placenta. IRSC Med. Sci, Lib. Compend. 10, 175; Dao, D.D., Partridge, C.A., Kurosky, A., Awasthi, Y.C., 1984. Human glutathione transferase. Characterization of the anionic forms from lung and placenta. Biochem. J. 221, 33-41), but poorly with human liver cytosol. The affinity-isolated protein fraction from whole intestine contained proteins that were immunologically related to all four major classes of human GSTs tested. N-terminal sequence analysis of the predominant band obtained by 2D electrophoresis indicated a marked homology (63-70% identical) to mammalian pi form GST isozymes and very strong similarity (80%) to a salmon hepatic GST that was designated a pi form (Dominey, R.J., Nimmo, I.A., Cronshaw, A.D., Hayes, J.D., 1991. The major glutathione S-transferase in salmonid fish livers is homologous to the mammalian pi class GST. Comp. Biochem. Physiol. (B) 100 (1), 93-98). Other bands contained insufficient protein for N-terminal analysis. Taken together, these results indicate that the predominant intestinal GST isoform is related to the pi-class enzymes, but minor GSTs related to other families are also present.