Pitrilysin (, Escherichia coli protease III, protease Pi, proteinase Pi, PTR, Escherichia coli metalloproteinase Pi) is an enzyme. This enzyme catalyses the following chemical reaction:
Preferential cleavage of -Tyr<sup>16</sup>- Leu- and -Phe<sup>25</sup>- Tyr-bonds of oxidized insulin B chain. Also acts on other substrates of less than 7 kDa such as glucagon