LOCUSTA-AKH-III AND RELATED PEPTIDES CONTAINING 2 TRYPTOPHAN RESIDUESHAVE UNUSUAL CD SPECTRA

Locusta adipokinetic hormone-III (AKH-III, <QLNFTPWWa) and three analo gues have been studied by CD spectroscopy. The AKH peptides examined i n which the tryptophan residues are adjacent present a distinctive neg ative-positive CD signature, in aqueous solution, that increases at lo w temperatures in ethanediol/water. In the presence of 0.6% SDS, a pos itive-minus CD is observed. The separation of the two tryptophan resid ues by an aliphatic amino acid results in a CD, in aqueous solution in verted from negative to positive CD at similar to 225nm. For the pepti des with two adjacent tryptophan residues, the bisignate nature of thi s tryptophan-based CD at lower temperatures or in SDS indicates that t he indole/indole orientation can adopt two limiting conformations. The re is a correlation between the size of the negative CD at 225nm and t he AKH peptide potency which may indicate a preferred indole/indole or ientation by the receptor. (C) 1996 Academic Press. Inc.