Kinetics of Angiotensin I alteration of conformation on different hydrophobic interaction chromatographic surfaces.

In the present study, Angiotensin I (Ang I) will be used as model peptide to assess on-column alteration of conformation phenomena. Adsorptive behavior of Ang I on various commercial hydrophobic interaction surfaces (Butyl, Octyl and Phenyl - Sepharose), under different conditions, was investigated. In order to calculate the cis-trans isomerization rate constants of Ang I on the stationary phase's surface, the first and second moments of the proline peptide elution profiles were determined.

Angiotensin I retention behavior on Butyl-Sepharose under linear loading chromatographic conditions.

Adsorption behavior of angiotensin I on a commercial Butyl-Sepharose support has been studied in function of temperature and ammonium sulphate concentration. Under isocratic elution conditions and at the higher salt concentrations, a characteristic of the chromatographic performance of angiotensin I was the broadness of the corresponding peak and in most of the cases the appearance of two peaks. These results have been interpreted in terms of on-column cis-trans isomerization of angiotensin I (a proline containing polypeptide) followed by its "re-conformation" after the interaction with the support.