Abstract
Excess heavy metals are highly toxic. Different organisms appear to have evolved different mechanisms for the detoxification of heavy metals in excess. In response to excessive uptake of heavy metals, plants and certain fungi produce metal-binding peptides that have the general structure (γ-Glutamyl-cysteinyl) n-Glycine, (γ-EC)nG, with n = 2 to 11. Cadmium incorporated into the cell is detoxified by (γ-EC)nG. The idea of using some hyperaccumulative and hypertolerant plants to remove excessive soil metals, phytoremediation, has increasingly been examined. In this study, we characterized the enzyme responsible for (γ-EC)nG synthesis in rice root. Optimum pH of the enzyme is 8.5 and incubation period and GSH concentration optima are 2 h and 10 mM, respectively. The (γ-EC)nG synthesis activity increased with Cd and Zn addition. Because the specific inhibitor of carboxypeptidase inhibited (γ-EC)nG synthesis activity, it assumed that at least one of the (γ-EC)nGsynthase in the rice root may be carboxypeptidase.
