Inactivation of peptidylglycine α-hydroxylating monooxygenase by cinnamic acid analogs.

Peptidylglycine alpha-amidating monooxygenase (PAM) is a bifunctional enzyme that catalyzes the final reaction in the maturation of alpha-amidated peptide hormones. Peptidylglycine alpha-hydroxylating monooxygenase (PHM) is the PAM domain responsible for the copper-, ascorbate- and O-2-dependent hydroxylation of a glycine-extended peptide. Peptidylamidoglycolate lyase is the PAM domain responsible for the Zn(II)-dependent dealkylation of the alpha-hydroxyglycine-containing precursor to the final alpha-amidated peptide. We report herein that cinnamic acid and cinnamic acid analogs are inhibitors or inactivators of PHM. The inactivation chemistry exhibited by the cinnamates exhibits all the attributes of a suicide-substrate. However, we find no evidence for the formation of an irreversible linkage between cinnamate and PHM in the inactivated enzyme. Our data support the reversible formation of a Michael adduct between an active site nucleophile and cinnamate that leads to inactive enzyme. Our data are of significance given that cinnamates are found in foods, perfumes, cosmetics and pharmaceuticals.