Cyclic tetrapeptides with sequences related to HC toxin. Conformations and cation binding

Abstract
Peptides with sequences related to HC toxin (cyclo(LAla-DAla-L-Aoe-DPro)) can adopt a conformation locked by three .gamma. turns. A "structure.sbd.spectroscopy characteristics" relationship is proposed. These peptides can complex Mg++ cations and the binding is accompanied by a transconformation of the peptide backbone. The relevancewith the biological activity of the toxin is discussed.