Purification and characterization of a lethal toxin from the venom of Heloderma horridum horridum

A lethal toxin was isolated from the venom of Heloderma h. horridum by gel filtration and ion-exchange chromatography. Molecular weight of the purified toxin was determined to be 28 kDa under reducing and nonreducing conditions. Biological activity, assayed by i.v. routes of injection, shows an LD50 for this preparation of 0.135 micrograms/g. Additionally, the toxin possesses an inhibitory effect on direct electrical stimulation of the isolated mouse hemi-diaphragm. However, neither hemorrhagic nor hemolytic activities were detected. Phospholipase A2 activity, proteolytic activity and arginine esterolytic activity were absent. The amino acid composition of the lethal toxin and the NH2-terminal sequence up to residue number 33 were determined. Neither show similarities to other components from H. h. horridum venom.