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 isofo rms (GSTs) have been studied for their ability to conjugate these substrate s with reduced glutathione (GSH). Three cDNAs, encoding corn GST subunits o f 29, 27, and 26 kDa, respectively, were cloned into expression systems in Escherichia coli. N-terminal 6xHis-tagged recombinant GST isoforms I, II, I II, and IV were purified with nickel-nitrilotriacetic acid (Ni-NTA) metal-a ffinity chromatography and were analyzed biochemically. As the corn enzymes , each recombinant GST isoform also consists of two subunits. Using three d ifferent GST-substrates, recombinant isoforms showed similar substrate spec ificities as natural corn GSTs. Some GST isoforms may be involved in the de fense response to oxidative stress in plants. Besides standard GST activiti es, inactivation of endogenous, toxic alpha,beta-unsaturated aldehydes was measured. Furthermore two recombinant GST isoforms (GST II and GST IV) show ed high glutathione peroxidase activity using three different organic hydro peroxides as substrates. Apparently, GST isoforms including the 27-kDa subu nit show glutathione peroxidase activity. (C) 1999 Academic Press.