Structural differences between erabutoxins in aqueous solution and in crystalline states.

The snake venom toxins erabutoxin a and b, have been studied in detail in aqueous solution over a wide pH range by proton NMR spectroscopy. Great care has been taken particularly to assign and locate in the structure residue histidine-7 with reference to other amino-acid sidechains. It lies in a pocket away from the surface in agreement with its lack of chemical reactivity. The data are not consistent with two structure determinations in crystals by X-ray diffraction. The aqueous solution conformation explains in greater depth the observed essentially of amino acids to the activity of the toxin.