Glutathione, S-substituted glutathiones, and leukotriene C 4 as substrates for peptidylglycine α-amidating monooxygenase

Abstract

The C-terminal α-amide moiety of most peptide hormones arises by the posttranslational cleavage of a glycine-extended precursor in a reaction catalyzed by bifunctional peptidylglycine α-amidating monooxygenase (PAM). Glutathione and the S-alkylated glutathiones have a C-terminal glycine and are, thus, potential substrates for PAM. The addition of PAM to glutathione, a series of S-alkylated glutathiones, and leukotriene C 4 results in the consumption of O 2 and the production of the corresponding amidated peptide and glyoxylate. This reaction proceeds in two steps with the intermediate formation of a C-terminal α-hydroxyglycine-extended peptide. Amidated glutathione (γGlu-Cys-amide) is a relatively poor substrate for glutathione S-transferase with a V/ K value that is 1.3% of that for glutathione. Peptide substrates containing a penultimate hydrophobic or sulfur-containing amino acid exhibit the highest ( V/ K) app values for PAM-catalyzed amidation. The S-alkylated glutathiones incorporate both features in the penultimate position with S-decylglutathione having the highest ( V/ K) app of the substrates described in this report.