| Abstract: | A protein isolated from timber rattlesnake (Crotalus horridus horridus) venom by ion-exchange and high-pressure liquid chromatography is hemorrhage inducing and lethal to mice (LD50 of 10 micrograms/g of body weight). It is a Ca2+- and Zn2+-containing proteinase and has the ability to hydrolyze hide powder azure. Atomic absorption spectroscopy shows 2.5 Ca2+ and 1 Zn2+ per protein monomer. The proteinase activity is destroyed by incubation with disulfide-reducing agents and by dialysis against ethylenediaminetetraacetate. Coincident with the loss of proteinase activity is a corresponding loss of lethal and hemorrhagic activities, suggesting that all three are related. Attempts to replace the metals and restore activity have been unsuccessful. Amino acid analysis and isoelectric focusing reveal that this component is an acidic protein (pI = 5.1) containing about 20 disulfide bonds and 507 residues. Reduction of one disulfide bond per molecule decreases proteinase activity by 50% while reduction of eight disulfide bonds decreases activity by 80%. Loss of hemorrhagic activity parallels the decrease in proteinase activity. |
