title: Reaction of proton pump inhibitors with model peptides results in novel products.
abstract: The proposed mechanism for proton pump inhibitors (PPIs) is that PPIs are activated at low pH to the sulfenamide form, which reacts with the sulfhydryl group of cysteine(s) at the active site of the proton pump, to produce reducible disulfide-bonded PPI-proton pump conjugates. However, this mechanism cannot explain the observations that some PPI-protein conjugates are irreducible. This study was designed to investigate the chemistry of the irreducible conjugates by mass spectrometry, using three PPIs and 17 cysteine-containing peptides. While some peptides favored the formation of reducible PPI-peptide adduct, the other peptides mainly produced irreducible adducts. Characterization of the irreducible adduct revealed that the irreducible bonding required the participation of both a sulfhydryl group and a nearby primary amino group. High resolution mass spectrometry suggested a molecular structure of the irreducible adduct. These results suggested a reaction mechanism in which the PPI pyridone form reacted with an amino group and a sulfhydryl group to form an irreducible adduct. The irreducible adduct becomes the dominant product over time because of the irreversible nature of the pyridone-mediated reaction. These findings may explain the irreducible inhibition of H/K-ATPase by PPIs and their relatively slow biological turnover in vivo. [Supplementary materials: available only at http://dx.doi.org/10.1254/jphs.13058FP].
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA.
authors.forename: Charles
authors.initials: C
authors.lastname: Watson
authors.forename: Lixin
authors.initials: L
authors.lastname: Zhu
authors.forename: Shenheng
authors.initials: S
authors.lastname: Guan
authors.forename: Terry E
authors.initials: TE
authors.lastname: Machen
authors.forename: John G
authors.initials: JG
authors.lastname: Forte
mesh_terms: D053799:2-Pyridinylmethylsulfinylbenzimidazoles / Q000737:chemistry / Q000494:pharmacology; D020134:Catalytic Domain; D003545:Cysteine / Q000737:chemistry*; D004791:Enzyme Inhibitors; D017506:H(+)-K(+)-Exchanging ATPase; D006863:Hydrogen-Ion Concentration; D064747:Lansoprazole / Q000737:chemistry / Q000494:pharmacology; D013058:Mass Spectrometry; D015394:Molecular Structure; D009853:Omeprazole / Q000737:chemistry / Q000494:pharmacology; D000077402:Pantoprazole; D010455:Peptides / Q000737:chemistry*; D054328:Proton Pump Inhibitors / Q000737:chemistry* / Q000494:pharmacology*; D011728:Pyridones; D013416:Sulfamerazine
chemical_list: D053799:2-Pyridinylmethylsulfinylbenzimidazoles; D004791:Enzyme Inhibitors; D010455:Peptides; D054328:Proton Pump Inhibitors; D011728:Pyridones; C471392:sulfenamide; D064747:Lansoprazole; D000077402:Pantoprazole; D017506:H(+)-K(+)-Exchanging ATPase; D003545:Cysteine; D009853:Omeprazole; D013416:Sulfamerazine