In the formation of mercapturic acid from glutathione conjugates, first a glutamate residue is hydrolysed from the conjugate then a glycine residue (Gly). The dipeptidases 1,2 and 3 (DPEP1,2,3) perform this second hydrolysis. They are membrane-bound, homodimeric enzymes which require zinc ions for activity. DPEP1 has been characterised (Satoh et al. 1993, 1994, Nitanai et al. 2002) whereas DPEP2 and 3 are thought to function as DPEP1 based on similarity.