THE ROLE OF THE DISULFIDE BONDS IN ENDOTHELIN-1

The smooth muscle contracting peptide endothelin-1 is characterized by the presence of two disulphide bonds and their importance for maintaining the agonist activity of the peptide was examined by synthesizing analogues of endothelin-1 lacking one or the other, or both, of these bonds. The circular dichroic spectra of these analogues (in which alanine residues replaced the appropriate cystines), [Ala1,15]-, [Ala3,11]- and [Ala1,3,11,15]-endothelin-1 had features in common with that of endothelin-1. All three analogues exhibited at least some agonist activity in guinea-pig isolated trachea, but surprisingly endothelin-1 was a partial agonist in comparison with the analogue [Ala3,11]endothelin-1: The disulphide bonds are therefore not absolutely essential for maintaining the tertiary structure necessary for agonist activity at endothelin-1 receptors in all tissues.