Gamma-Glutamyltransferase 3 (gGT3)

GGT3 is localized to the vacuole based on organelle-targeting programs, subcellular distribution of GFP fusion proteins during transient expression in onion epidermal tissues, and its ability to metabolize vacuolar substrates in Arabidopsis plants. 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.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.