Mammalian γ-glutamyltransferase (GGT) is a glycoprotein consisting of two subunits -a light chain and a heavy chain. The light chain contains the catalytic activity; the heavy chain anchors the protein to the membrane. GGT catalyzes the hydrolysis of the γ-glutamyl isopeptide bond of glutathione conjugates, releasing glutamic acid, or the transfer of the γ-glutamyl group to an acceptor substrate. The specificity of the enzyme for xenobiotic donor substrates has not been