SCHISTOSOMA-MANSONI - SINGLE-STEP PURIFICATION AND CHARACTERIZATION OF GLUTATHIONE-S-TRANSFERASE ISOENZYME-4

A soluble glutathione S-transferase isoenzyme, designated SmGST-4 was purified to apparent homogeneity in a single step from the cytosol of adult Schistosoma mansoni by selective elution of the enzyme from a glutathione-agarose affinity column using glutathione disulfide. SmGST-4, which comprised about 5% of the bound glutathione S-transferase activity, could be distinguished from the previously characterized glutathione S-transferase isoenzyme family (SmGST-1/2/3) by its unique Chromatographic behavior, lower subunit Mr (26,000), differences in substrate specificity and inhibitor sensitivity, and a lack of reactivity with antiserum to SmGST-3. The purified isoenzyme catalyzed the conjugation of several model xenobiotics including 1-chloro-2,4-dinitrobenzene, ethacrynic acid, and trans-4-phenyl-3-buten-2-one. Like the SmGST-1/2/3 isoenzyme family, SmGST-4 failed to catalyze the conjugation of a model epoxide substrate, 1,2-epoxy-3-(p-nitrophenoxy)propane. Because glutathione S-transferases from other organisms play a role in protecting cells against the toxic products of lipid peroxidation, SmGST-4 and the members of the SmGST-1/2/3 isoenzyme family were tested for their capacity to reduce cumene hydroperoxide and to catalyze the conjugation of 4-hydroxyalk-2-enals. Although all four isoenzymes catalyzed both reactions, the specific activity of SmGST-1, SmGST-2, and SmGST-3 toward cumene hydroperoxide was at least 10-fold greater than that of SmGST-4. In contrast, the latter more effectively conjugated a homologous series of 4-hydroxyalk-2-enal isomers. For example, the specific activity of SmGST-4 toward 4-hydroxynon-2-enal (10.8 μmol · min-1 · mg protein-1), the isomer formed under physiological conditions, was about 5-fold greater than that of SmGST-1 and 12-fold greater than that of the major isoenzyme SmGST-3. These results are consistent with a multifunctional role for schistosome glutathione 5-transferases in protecting the parasite against both xenobiotics and toxic endogenous products of lipid peroxidation. © 1992.