GSTp (Glutathione S-transferase P) is an enzyme that plays an important role in detoxification by catalyzing the conjugation of many hydrophobic and electrophilic compounds with reduced glutathione. GSTP1 is identified as a CDK5 (Cyclin dependent kinase-5) regulatory protein, and is thought to regulates negatively CDK5 activity via p25/p35 translocation. GSTP1 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 chinese hamster GSTP1, mix gentliy. Incubated at 37℃ for 5min, then read at a wavelength of 340 nm. The specific activity of recombinant chinese hamster GSTp1 is >6500 pmol/min/μg.