Effects of pH and temperature on cardioactive polypeptides from sea anemones: A 1H‐nmr study

Abstract

The effects of pH and temperature on the 300‐MHz 1H‐nmr spectra of three cardioactive polypeptides from sea anemones, anthopleurin‐A from Anthopleura xanthogrammica (AP‐A) and Anemonia sulcata toxins I and II (ATX I and II), are described. AP‐A and ATX II exhibit major spectral heterogeneity. Evidence from the pH and temperature studies and from high performance liquid chromatography indicates that this heterogeneity is conformational rather than chemical in origin. By contrast, purified isotoxins of ATX I show no evidence of conformational heterogeneity. The pKa values of most of the ionizable groups in these polypeptides are not strongly perturbed by interactions in the tertiary structure,..