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A ligand function of glutathione S-transferase
1Department of Physiology and Biochemistry, University of Konstanz, Konstanz, Germany.
Summary
Plant glutathione S-transferases (GSTs) bind tetrapyrroles non-covalently, inhibiting their activity and protecting key molecules like protoporphyrinogen from damaging oxidation.
Area of Science:
- Plant biochemistry
- Enzymology
- Molecular biology
Background:
- Glutathione S-transferases (GSTs) are crucial plant enzymes involved in metabolism and stress defense.
- Their specific roles, especially concerning reactive oxygen species and novel reactions, require detailed investigation.
Purpose of the Study:
- To assign specific reactions, including novel ones, to particular maize GST isoforms.
- To investigate the interaction between GST isoforms and tetrapyrroles from the chlorophyll biosynthesis pathway.
Main Methods:
- Recombinant expression of maize GST isoforms in transformed E. coli.
- Purification of GSTs using N-terminal His tags and affinity chromatography.
- Enzymatic assays to determine substrate interactions and inhibition kinetics.
Main Results:
- Maize GSTs bind tetrapyrroles (e.g., protoporphyrin IX, Mg-protoporphyrin) non-covalently, not conjugating them with glutathione.
- This binding non-competitively inhibits substrate (1-chloro-2,4-dinitrobenzene) and competitively inhibits glutathione conjugation.
- Specific GST dimers, GST 26/26 and GST 27/27, protect protoporphyrinogen and hemin, respectively, from degradation and oxidation.
Conclusions:
- Plant GSTs play a protective role by non-covalently binding tetrapyrroles, modulating their activity and preventing phytotoxic reactive oxygen species formation.
- GSTs facilitate the safe transport of protoporphyrinogen to mitochondria for cytochrome processing.