Gamma-glutamyltransferase 6Gamma-glutamyltransferase 6 is a protein that in humans is encoded by the GGT6 gene.FunctionGGT6 belongs to the gamma-glutamyltransferase gene family. GGT is a membrane-bound extracellular enzyme that cleaves gamma-glutamyl peptide bonds in glutathione and other peptides and transfers the gamma-glutamyl moiety to acceptors. GGT is also key to glutathione homeostasis because it provides substrates for glutathione synthesis.