Abstract
Enzymes responsible for catabolism of glutathione are not clear in higher plants. In mammals and microbes, γ-glutamyltransferase (GGT) catalyzes the transfer or the hydrolysis of γ-glutamyl moiety of γ-glutamyl-compounds. In several plants, GGT activities were detected both in the soluble fraction (s-GGT) and in the fractions solubilized from the pellet with NaCl (b-GGT). We examined the localization of GGTs in radish plants and concluded that s-GGT is present in the soluble fraction and b-GGT is localized to the cell wall. 4 isozymes (2 s-GGTs and 2 b-GGTs) were purified from radish cotyledons. Enzymatic properties were similar among s-GGTs and as so among b-GGTs, but differed between s-GGTs and b-GGTs. We cloned 2 radish GGT cDNAs and analysed their expression. The transgenic tobacco plants overexpressing these genes were produced. GGT activities were detected in the bound fraction and properties of the recombinant enzymes were similar to those of radish b-GGTs.
