Purification and characterization of corn glutathione S-transferase

Area of Science:

• Biochemistry
• Plant Science
• Enzymology

Background:

• Glutathione S-transferases (GSTs) are crucial enzymes involved in detoxification pathways in plants.
• Corn (Zea mays) possesses GSTs that play a role in herbicide metabolism, but specific enzyme activities and their induction are not fully characterized.

Purpose of the Study:

• To identify and purify distinct glutathione S-transferase (GST) enzyme activities from etiolated corn tissue.
• To characterize the properties and substrate specificities of the purified GST enzymes.
• To investigate the role of GST II in response to chemical antidote treatment for herbicide protection.

Main Methods:

• Enzyme purification using chromatography techniques (Sephadex G-100).
• Enzyme characterization through molecular weight determination (SDS-PAGE).
• In vitro enzymatic assays using alachlor as a substrate to measure GST activity.

Main Results:

• Two GST activities, GST I and GST II, were purified, constituting approximately 2% of soluble protein.
• GST I is constitutively present, while GST II is induced by chemical antidotes protecting against chloroacetanilide herbicides.
• Both enzymes exhibit molecular weights around 50,000 Da (native) and 29,000/27,000 Da (denatured), and catalyze glutathione conjugation with alachlor, inactivating the herbicide.

Conclusions:

• Corn possesses at least two distinct GST enzymes with differential expression patterns.
• GST II induction by antidotes suggests a role in enhancing herbicide resistance in corn.
• The enzymatic conjugation of glutathione to herbicides by these GSTs is a key detoxification mechanism in corn.