Association of glutathione peroxidase activity with an acidic glutathione S-transferase in carp liver

Carp liver contains a glutathione S-transferase isoenzyme which uses as bes t substrates 1-chloro-2,4-dinitrobenzene (CDNB) and cumene hydroperoxide, t hus showing selenium-independent glutathione peroxidase activity. This isoe nzyme accounts for about 15% of the total activity with CDNB and does not b ind to the affinity matrix of hexyl-S-glutathione Sepharose 6B. It has been partially purified by ionic exchange and gel filtration chromatographies a nd isoelectric focusing. The purified enzyme is an acidic protein of 55 kDa of relative molecular mass and has an isoelectric point at pH 5.4. Values of Km have been measured for both CDNB and reduced glutathione (GSH) substr ates. The best substrates are CDNB and cumene hydroperoxide, followed by et hacrynic acid and 1,2-epoxy-3-(p-nitrophenoxy)-propane. Hydrogen peroxide a nd 1,2-dichloro-4-nitrobenzene are not substrates and trans-4-phenyl-3-bute n-2-one is a very poor one. Among several glutathione S-transferase inhibit ors used, cibacron blue and rose bengal are the strongest; the herbicides, 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (Pyrazon), 2,4-dichlorophenoxy acetic acid (2,4-D), and 2-(2-methyl-4-chlorophenoxy) propionic acid (MCPA) are less effective.