Coordination-chemistry study of polypeptides. III. protonation-deprotonation equilibrium study of synthetic alphaH -corticotropin1-32. Data on the pH-dependent conformation of corticotropin.

By potentiometric equilibrium measurements and the computer evaluation of experimental data, the protonation equilibrium constants of four fragments of corticotropin (ACTH), ACTH1-32. ACTH1-28, ACTH1-14 and ACTH1-4, were determined and assigned to the corresponding functional groups. From the dependence of the protonation constants on the length of the peptide chain, it was established which functional groups participate in the formation of intramolecular hydrogen-bonds in aqueous solutions at various pH. These results indicated a pH-dependent conformation of the molecule.