Glutathione transferases (GSTs) catalyze the transfer of glutathione to a variety of xenobiotic and toxic endogenous compounds. GSTs are phase H biotransformation enzymes and are proposed as biomarkers of environmental pollution. In this study, a cytosolic glutathione transferase (maGST) was purified from liver of the freshwater fish Monopterus albus by affinity chromatography. The maGST appeared to be a homodimer composed of two subunits each with a molecular weight of 26 kDa. This maGST showed high activity towards the substrates 1-chloro-2,4-dinitrobenzene (CDNB) and 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl). Kinetic analysis with CDNB as substrate revealed a K. of 0.28 mM and V-max of 15.68 mu mol/min per mg of protein. It had maximum activity in the pH range 7.0-7.5, a broad optimum T-m range of 30 degrees C-55 degrees C, and a high thermal stability with 77% of its initial activity at 45 degrees C. This high thermal stability of maGST could be related to the physiological adaptation of M albus to high temperatures in tropical and subtropical environments. (c) 2007 Elsevier Inc. All rights reserved.