Characterization of Two Myotoxic Proteins from Venom ofCrotalus viridis concolor

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Abstract
The fractionation of the previously unstudied venom for Crotalus viridis concolor (midget faded rattlesnake) provided a protein fraction (FD-1) that generated myotoxic responses from envenomated mice. Highly basic homologous myotoxic proteins have been purified from the protein fraction, FD-1. The two major components, designated myotoxin I and myotoxin II, have considerable sequence homology with crotamine from C. d. terrificus, myotoxin a from C. v. viridis and peptide c from C. v. helleri. The amino acid sequences of the toxins from C. v. concolor contain at least two more residues of amino acid than previously described homologous toxins and myotoxin II contains a sequence region with microheterogeneity. The myotoxins cause extensive damage to the sarcoplasmic reticulum as evidenced by electron microscopic studies of envenomated muscle. The destruction is comparable to that observed with the homologous toxins. Studies with isolated sarcoplasmic reticulum vesicles failed to demonstrate any significant changes in Ca2+-Mg2+-ATPase or in uptake or release of Ca2+. Current evidence indicates that a closely related group of homologous toxins are present in rattlesnake venoms but the biochemical mode of action of these proteins remains obscure.