CIRCULAR-DICHROISM STUDIES OF HUMAN BIG-ENDOTHELIN-1 (BIG ET-1)

The circular dichroism (CD) spectra of human endothelin (ET-1) and its precursor (Big ET-1) have been compared in order to provide informati on on the secondary structure of Big ET-1. It appears that the seconda ry structures of the common parts of the two molecules are very simila r and that the additional C-terminal residues in Big ET-1 may contain both helical and sheet components, information which may be of use in modeling studies of the Big ET-1 structure. In studies of the pH depen dence of the conformation of Big ET-1, it was found that Big ET-1 adop ts similar structures at pH 6.0 and 7.0, but has a subtly different co nformation at pH 8.0 that may result in a reduced susceptibility to pr oteolysis at this pH. This difference may be in the conformation of a turn-type structure, producing a less accessible peptide bond in the m olecule at the site of cleavage. (C) Munksgaard 1997.