The substrate specificities and subunit compositions of the hepatic glutathione S-transferases of rainbow trout (Salmo gairdneri).

Chromatofocusing separated the glutathione S-transferases of trout liver cytosol into species termed cationic (eluted from pH 8-5) and anionic (eluted by 1.0 M NaCl at pH 5). The cationic enzymes were separated from cytosol by S-hexylglutathione affinity chromatography, ultrafiltration and chromatofocusing (pH 9-7) into 4 major (C1, C2, C4 and C5) and 3 minor fractions. The anionic material was not purified in this way because only 50% of the activity bound to the S-hexylglutathione column. The major cationic enzymes had similar half-saturation concentrations for GSH (0.2 mM) and 1-chloro-2,4-dinitrobenzene (0.4 mM); those of the anionic material were higher (0.7 mM, 1.9 mM respectively). The substrate specificities of the cationic enzymes C1 and C2 were similar (e.g., conjugation of bromosulphophthalein) as were those of C4 and C5 (e.g., conjugation of 1,2-epoxy-3-(p-nitrophenoxy) propane). The anionic material had a different specificity (e.g., rapid conjugation of p-nitrobenzyl chloride). SDS-polyacrylamide gel electrophoresis showed C1 and C2 to be homodimers of subunit Mr 22,400, C4 to be a heterodimer (Mr's 22,400 and 24,500), and C5 predominantly an Mr 22,400 homodimer.