Novel insights into peptide amidation and amidating activity in the human circulation

C-terminal α-amidation is the final and essential step in the biosynthesis of several peptide hormones. Peptidylglycine α-amidating monooxygenase (PAM) is the only known enzyme to catalyse this reaction. PAM amidating activity (AMA) is known to be present in human circulation, but its physiological role and significance as a clinical biomarker remains unclear. We developed a PAM-specific amidation assay that utilizes the naturally occurring substrate Adrenomedullin-Gly (ADM-Gly, 1-53). Using our amidation assay we quantified serum amidating activities in a large population-based cohort of more than 4900 individuals. A correlation of serum amidating activity with several clinical parameters including high blood pressure was observed. Increasing PAM-AMA was an independent predictor of hard outcomes related to hemodynamic stress such as cardiovascular mortality, atrial fibrillation and heart failure during long-term follow-up (8.8 ± 2.5 years). Moreover, results from an animal study in rats utilizing recombinant human PAM provide novel insights into the physiological role of circulating PAM and show its potential significance in circulating peptide amidation.