Photochemically induced dynamic nuclear polarisation NMR study of the aromatic residues of sea-anemone polypeptide cardiac stimulants.
One-dimensional and two-dimensional photochemically induced dynamic nuclear polarisation (photo-CIDNP) nuclear magnetic resonance spectra have been recorded for the sea-anemone polypeptide cardiac stimulants anthopleurin-A and Anemonia sulcata toxins I and II. In anthopleurin-A and toxin II, all three Trp residues are accessible to the flavin dye, although Trp-23 in anthopleurin-A shows a weaker photo-CIDNP response than Trp-33 and Trp-45. Tyr-25 in anthopleurin-A also shows a strong response. In toxin I, Trp-23, Trp-33 and Tyr-45 (which replaces Trp in this molecule) are accessible to the dye. The pH dependences of the photo-CIDNP spectra of all three polypeptides have been examined. The response of Trp-33 increases significantly with pH. The two His residues of anthopleurin-A and toxin II display a response in their imidazole forms, but not their imidazolium forms. The surface accessibilities of Trp-23 and Trp-33 are discussed in relation to the interaction of these polypeptides with the Na+ channel.
Norton
R S
RS
Beress
L
L
Stob
S
S
Boelens
R
R
Kaptein
R
R
D000818:Animals; D002316:Cardiotonic Agents; D003063:Cnidaria / Q000032:analysis*; D009682:Magnetic Resonance Spectroscopy; D010455:Peptides; D010777:Photochemistry; D012615:Sea Anemones / Q000032:analysis*
D002316:Cardiotonic Agents; D010455:Peptides