Glutathione conjugates in the vacuole are degraded by gamma-glutamyl transpeptidase GGT3 in Arabidopsis.

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Ohkama-Ohtsu N, Zhao P, Xiang C, Oliver DJ

Glutathione conjugates in the vacuole are degraded by gamma-glutamyl transpeptidase GGT3 in Arabidopsis.

Plant J. 2007 Mar;49(5):878-88.

PubMed ID

17316176 [ View in PubMed

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Abstract

gamma-Glutamyl transpeptidase (GGT) is the enzyme responsible for breaking the gamma-glutamyl bond between Glu and Cys in glutathione (GSH). We are using this gene family to study GSH degradation in plants. There are four putative GGT genes in Arabidopsis, and one of them, GGT3 (At4g29210), is analyzed in this study. GGT3 is localized to the vacuole based on organelle-targeting programs, subcellular distribution of GFP fusion proteins during transient expression in onion (Allium cepa) epidermal tissues, and its ability to metabolize vacuolar substrates in Arabidopsis plants. While Northern blots and promoter:GUS expression patterns have suggested that GGT3 is transcribed at relatively high levels in all parts of the plant, a comparison of enzyme activities in different organs of wild-type and a ggt3 knockout mutant showed that GGT3 was a major contributor to total GGT activity in roots, but a relatively minor contributor in other tissues. Wild-type Arabidopsis plants treated with monobromobimane (mBB) form a fluorescent GSH-mBB conjugate that is moved into the vacuole and then metabolized to Cys-Gly-mBB and Cys-mBB in that order. The first step is catalyzed by GGT3, and GSH-mBB metabolism is completely blocked in the roots of ggt3 knockout plants. In ggt3 leaves, some GSH-mBB metabolism still proceeds using the apoplastic GGT1. This identifies GGT3 as catalyzing the obligate initial step in GSH conjugate metabolism, and suggests that it has an important role in protecting plants from some xenobiotic chemicals.

DrugBank Data that Cites this Article

Drug Targets

Drug	Target	Kind	Organism	Pharmacological Action	Actions
Glutathione	Gamma-glutamyltranspeptidase 1	Protein	Humans	Unknown	Not Available	Details