Characterization of Recombinant Corn Glutathione S-Transferase Isoforms I, II, III, and IV

Glutathione S-transferases (GSTs) are involved in detoxification of a wide variety of electrophilic compounds including herbicides. Several corn isoforms (GSTs) have been studied for their ability to conjugate these substrates with reduced glutathione (GSH). Three cDNAs, encoding corn GST subunits of 29, 27, and 26 kDa, respectively, were cloned into expression systems in Escherichia coli.N-terminal 6xHis-tagged recombinant GST isoforms I, II, III, and IV were purified with nickelnitrilotriacetic acid (Ni-NTA) metal-affinity chromatography and were analyzed biochemically. As the corn enzymes, each recombinant GST isoform also consists of two subunits. Using three different GST-substrates, recombinant isoforms showed similar substrate specificities as natural corn GSTs. Some GST isoforms may be involved in the defense response to oxidative stress in plants. Besides standard GST activities, inactivation of endogenous, toxic -unsaturated aldehydes was measured. Furthermore two recombinant GST isoforms (GST II and GST IV) showed high glutathione peroxidase activity using three different organic hydroperoxides as substrates. Apparently, GST isoforms including the 27-kDa subunit show glutathione peroxidase activity.