(biochemistry) An endopeptidase enzyme, found in the venom of the diamondback rattlesnake Crotalus atrox, that catalyzes the cleavage of His⁵-Leu, Ser⁹-His, His¹⁰-Leu, Ala¹⁴-Leu and Tyr¹⁶-Leu of insulin B chain.