Role of aspartate residues in the cardiac stimulatory activity of anthopleurin-A.

Modification of the polypeptide anthopleurin-A with a carbodiimide and glycine ethyl ester leads to the addition of nearly two Gly to AP-A. Limited amino acid sequence analysis shows that modification occurs principally at Asp-7 and Asp-9. The modified derivative shows no cardiac stimulatory activity. 1H nuclear magnetic resonance and circular dichroism spectra of the derivative show that its conformation is significantly altered. Thus, the Asp residues are essential for the cardiac stimulatory activity of AP-A, as well as for maintaining its native conformation.