Locusta-AKH-III and related peptides containing two tryptophan residues have unusual CD spectra.
Locusta adipokinetic hormone-III (AKH-III, < QLNFTPWWa) and three analogues have been studied by CD spectroscopy. The AKH peptides examined in which the tryptophan residues are adjacent present a distinctive negative-positive CD signature, in aqueous solution, that increases at low temperatures in ethanediol/water. In the presence of 0.6% SDS, a positive-minus CD is observed. The separation of the two tryptophan residues by an aliphatic amino acid results in a CD, in aqueous solution inverted from negative to positive CD at approximately 225nm. For the peptides with two adjacent tryptophan residues, the bisignate nature of this tryptophan-based CD at lower temperatures or in SDS indicates that the indole/indole orientation can adopt two limiting conformations. There is a correlation between the size of the negative CD at 225 nm and the AKH peptide potency which may indicate a preferred indole/indole orientation by the receptor.
Lee
M J
MJ
Department of Biology, Birkbeck College, University of London, England.
Drake
A F
AF
Goldsworthy
G J
GJ
D000595:Amino Acid Sequence; D000818:Animals; D002942:Circular Dichroism; D006110:Grasshoppers / Q000737:chemistry*; D007301:Insect Hormones / Q000737:chemistry*; D008823:Micelles; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry; D013696:Temperature; D014364:Tryptophan / Q000737:chemistry*; D014867:Water
D007301:Insect Hormones; D008823:Micelles; D014867:Water; D012967:Sodium Dodecyl Sulfate; D014364:Tryptophan