Endopeptidase that degrades small peptides of less than 7 kDa, such as glucagon and insulin. Preferential cleavage of 16-Tyr-|-Leu-17 and 25-Phe-|-Tyr-26 bonds of oxidized insulin B chain. Also acts on other substrates of Mw less than 7 kDa such as insulin and glucagon. Binds 1 zinc ion per subunit. Monomer. Belongs to the peptidase M16 family.