Molecular characterization of corn glutathione S‐transferase isozymes involved in herbicide detoxication

Corn ( Zea mays L.) glutathione S‐transferases (EC 2.5.1.18) have attracted interest, in part, due to their involvement in the metabolism of several herbicides, including atrazine and alachlor. Three corn, glutathione S‐transferases have been purified, and cDNA clones have been isolated and sequenced for two of these, GST I and GST III. In addition to showing some amino acid sequence similarity to each other, the two sequenced corn glutathione S‐transferases also show some similarity to rat and human enzymes. The corn glutathione S‐transferases responsible for atrazine tolerance have not yet been purified or cloned, but purification attempts indicate that corn has two glutathione S‐transferases with activity towards atrazine. While many glutathione S‐transferases from various organisms have been detected by using 1‐chloro‐2,4‐dinitrobenzene as a substrate, the atrazine‐specific glutathione S‐transferases have very little or no activity with 1‐chloro‐2,4‐dinitrobenzene. This shows the importance of assaying with a variety of substrates when characterizing glutathione S‐transferases.