Purification and partial characterization of glutathione transferase from the teleost Monopterus albus

Glutathione transferases (GSTs) catalyze the transfer of glutathione to a variety of xenobiotic and toxic endogenous compounds. GSTs are phase II 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 Km of 0.28 mM and Vmax of 15.68 μmol/min per mg of protein. It had maximum activity in the pH range 7.0–7.5, a broad optimum Tm range of 30 °C–55 °C, and a high thermal stability with 77% of its initial activity at 45 °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.