γ-Glutamyl transpeptidase (EC 2.3. 2.2; GGT) catalyses hydrolysis of γ-glutamyl linkages in γ- glutamyl peptides and transfer of the γ-glutamyl group to amino acids and peptides. Although plant γ-glutamyl peptide metabolism is important in biosynthesis and metabolism of secondary products and xenobiotics, plant GGTs are poorly characterised. We purified a membrane-associated GGT from sprouting onion bulbs that catalyses transpeptidation of ...