Carboxy-terminal amidation is an essential posttranslational modification for numerous neuronal and endocrine peptides.It is catalyzed by peptide α-amidating monooxygenase (PAM),in a two-step reaction. Peptidylglycine α-hydroxylating monooxygenase(PHM) and peptidyl-hydroxyglycine -α-amidating lyase(PAL) act in one of the two step.PHM catalytic core is composed of two nine-stranded β-sandwich domains similar in three-dimessional structure.Each domain contains an activity center with a copper coordinated by three conserved His or two His and a Met residues.In the reaction cycle of producing peptidyl α-hydroxyglycine,the two coppers are reduced independently by ascorbate,and they transfer one electron each to molecular oxygen.