Fig. 1

Schematic representation of the α-amidation process in cells. The α-amidation process is a highly specific enzyme-dependent post-translational modification need for converting prohormones into functional peptide products in neurosecretory cells. Panel a depicts the specific processing of large propeptide precursor proteins containing active peptide sequences (Peptide A, Peptide B) via PC1/PC3 proconvertase activity alone (Peptide A) or together with the functional activity peptidylglycine α-amidating monooxygenase (PAM) (Peptide B). Panel b illustrates the sequential steps of PAM-related bifunctional activity (EC 1.14.17.3) which includes the peptidylglycine α-hydroxylating monooxygenase (PHM) activity depicted in Step 1 and the peptidyl-α-hydroxyglycine-α-amidating lyase (PAL) activity depicted in Step 2. As shown, two molecules of ascorbate are oxidized to form two molecules of semidehydroascorbate during the reduction of two enzyme-bound Cu(II) atoms [E-Cu (II)] into two enzyme-bound Cu(I) atoms [E-Cu (I)] as previously described [10] (for specific details see text in “Background”)