biostudies-literatureChitta RKNCRR NIH HHSNIGMS NIH HHS1813-20https://www.ebi.ac.uk/biostudies/studies/S-EPMC2767204biostudies-literatureUnknown20(10)We describe the use of H/D amide exchange and electrospray ionization mass spectrometry to study, in organic solvents, the pentadecapeptide gramicidin as a model for protein self association. In methanol-OD, all active H's in the peptide exchange for D within 5 min, indicating a monomer/dimer equilibrium that is shifted towards the fast-exchanging monomer. H/D exchange in n-propanol-OD, however, showed a partially protected gramicidin that slowly converts to a second species that exchanges nearly all the active hydrogens, indicating EX1 kinetics for the H/D exchange. We propose that this behavior is the result of the slower rate of unfolding in n-propanol compared with that in methanol. The rate constant for the unfolding of the dimer is the rate of disappearance of the partially protectedJournal of the American Society for Mass SpectrometryThe gramicidin dimer shows both EX1 and EX2 mechanisms of H/D exchange.PMC27672042P41RR000954P41 GM103422P41 RR000954P41 RR000954-317532Rempel DLGross MLChitta RKfalseThe gramicidin dimer shows both EX1 and EX2 mechanisms of H/D exchange.We describe the use of H/D amide exchange and electrospray ionization mass spectrometry to study, in organic solvents, the pentadecapeptide gramicidin as a model for protein self association. In methanol-OD, all active H's in the peptide exchange for D within 5 min, indicating a monomer/dimer equilibrium that is shifted towards the fast-exchanging monomer. H/D exchange in n-propanol-OD, however, showed a partially protected gramicidin that slowly converts to a second species that exchanges nearly all the active hydrogens, indicating EX1 kinetics for the H/D exchange. We propose that this behavior is the result of the slower rate of unfolding in n-propanol compared with that in methanol. The rate constant for the unfolding of the dimer is the rate of disappearance of the partially protected2009-01-01T00:00:00Z2009 Oct2025-04-22T01:05:38.066Z2019-03-27T00:26:09ZS-EPMC27672041963155610.1016/j.jasms.2009.05.017