EC 3.4.24.46; other name: proteinase II; a metalloendopeptidase that catalyses the cleavage of Phe1-|-Val2, His5-|-Leu6, His10-|-Leu11, Ala14-|-Leu15, Leu15-|-Tyr16, and Tyr16-|-Leu17 in the insulin B-chain. Zn2+ and Ca2+ are cofactors. It is a snake venom proteinase whose natural substrate(s) are protease inhibitor(s), such as the serpins.