Glutathione S-Transferases (GSTs) are members of the phase II detoxification enzyme family that conjugate glutathione to various electrophilic compounds, including metabolites generated by oxidative processes in the body, environmental toxins or carcinogens, and anti-cancer drugs. GSTM1 is a cytosolic protein that belongs to the mu class of the GST superfamily. GSTM1 catalyze the endogenous glutathione conjugation 1-Chloro-2,4-dinitrobenzene (CDNB), which can increase in the absorbance at 340 nm. The reaction was performed in adding 10 μl 200 mM glutathione (reduced) and 10 μl 100 mM CDNB in 980 μl 100 mM NaH2PO4 (pH7.0), rapidly mixed. Then add 50 μl mixed substrates to 50 μl different concentrations of recombinant chicken GSTM1, mix gently. Incubated at 37℃ for 5min, then read at a wavelength of 340 nm. The specific activity of recombinant chicken GSTM1 is >2500 pmol/min/μg.