GSTa3 (Glutathione S-transferase a3) is an enzyme that plays an important role in detoxification by catalyzing the conjugation of many hydrophobic and electrophilic compounds with reduced glutathione. This subfamily of enzymes has a particular role in protecting cells from?Reactive Oxygen Species?and the products of peroxidation. Polymorphisms in this gene influence the ability of individuals to metabolize different drugs. GSTa3 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 rat GSTa3, mix gently. Incubated at 37℃ for 5min, then read at a wavelength of 340 nm. The specific activity of recombinant rat GSTa3 is >37000 pmol/min/μg.