Figure 2.

Endogenous cleavage of an enzyme substrate containing a targeting element and a reporter group in the enzymatic site of porcine APN. The substrate is oriented in the enzyme active site by residues A₃₄₈, E₃₈₄, and Y₄₇₂. A catalytic water is activated by a zinc cation and E₃₅₀. The water then attacks the substrate carbonyl, and E₃₈₄ shuttles a proton from the catalytic water to the leaving nitrogen [33].