Separation of enkephalin degradation products by ligand-exchange chromatography

Enkephalin degradation products can be accurately analyzed by cascade chromatography through XAD polystyrene and copper--Chelex columns. One of the main degradation products generated during the incubation of enkephalin with rat striatal membranes, the N-terminal amino acid Tyr, is absorbed quantitatively on the copper--Chelex columns whereas the minor, but probably specific, product Tyr--Gly--Gly is not.