Conformation of corticotropin. An infrared spectrometry study of hydrogen exchange kinetics

1H--2H exchange kinetics of the peptide hydrogens in corticotropin have been examined in 2H2O and CF3C2H2O2H solutions by means of infrared absorption measurements. In aqueous solution, around pH 3, the experimental data suggest a partially ordered structure, since in the two corticotropins 1--24 and 1--32 about 6 slowly exchanging peptide protons are numbered. These might belong to the N-terminal part of the molecule. The C-terminal 25--32 octapeptide segment appears to be unordered and slightly destabilizes the overall hormone conformation. For corticotropin1--24 in CF3C2H2O2H, the qualitative interpretation of infrared spectra and the quantitative analysis of exchange data give evidence of a strong stabilization: a predominantly alpha-helical structure is induced by trifluoroethanol.