title: Studies on the chemical modification of hemorrhagic toxin I from five pace snake (Agkistrodon acutus) venom.
abstract: The chemical modification of hemorrhagic toxin I (AaHI) from Agkistrodon acutus has been studied. Inactivation was observed upon modification of 3 out of 7 histidine residues with diethyl pyrocarbonate. The His residues are deblocked, accompanied by a return of activity, upon treatment with neutral hydroxylamine. The circular dichroism and fluorescence spectra of diethyl pyrocarbonate inactivated toxin and the native toxin are the same, indicating that modification with diethyl pyrocarbonate does not cause any gross change in the structure of the protein. At least one His residue may thus play an essential role in the enzyme activity. Reaction of the toxin with N-bromosuccimide abolished the enzyme activity, with modification of Trp, Tyr and His residues. The loss of Trp did not parallel the inactivation. Hydrogen peroxide, dioxane and 2-hydroxy-5-nitrobenzyl-bromide treatment damaged the Trp residues, but did not affect the activity. Therefore, the modified tryptophan side chains are not essential for activity. Modification of 2.5-3.0 Tyr residues out of 9 with acetylimidazole did not affect the enzyme activity, nor did nitration of the toxin with tetranitromethane. The reactive tyrosines are apparently not essential.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D055598:Chemical Phenomena; D002621:Chemistry; D002942:Circular Dichroism; D003435:Crotalid Venoms / Q000032:analysis*; D010084:Oxidation-Reduction; D013050:Spectrometry, Fluorescence
chemical_list: D000596:Amino Acids; D003435:Crotalid Venoms; C032814:hemorrhagin components (Crotalid)