EC 3.4.24.45; other names: Crotalus atrox metalloendopeptidase F; hemorrhagic toxin F; a snake-venom enzyme that catalyses the cleavage of Val2-|-Asn3, Gln4-|-His5, Leu6-|-Cys7, His10-|-Leu11, Ala14-|-Leu15, and Tyr16-|-Leu17 bonds in the insulin B-chain. It is a zinc-requiring enzyme.