Substrate specificity of porcine pancreatic kallikrein

The primary specificity of porcine pancreatic kallikrein is directed predominantly against arginyl and much less so against lysyl bonds. In addition, the enzyme exhibits pronounced secondary specificity for a bulky residue, preferentially phenylalanine, in position P2 of substrates. This feature is found also in porcine submandibular and urinary and in human urinary kallikrein, but not in bovine trypsin. Residues in P3 and P1' and P1' to P3' also affect hydrolysis by pancreatic kallikrein distinctly more than tryptic hydrolysis. The hexapeptide Pro-Phe-Arg-Ser-Val-Gln with the sequence of bovine kininogen around the C-terminus of kinin contains all the structural elements essential for the interaction with kallikrein, and even glutamine appears dispensable. In contrast to ester models for this site, peptidyl methionine esters with the structure of kininogen towards the N-terminus of kinin, notably bulky leucine in P2, are very poor kallikrein substrates, and appear to be of no value as models for the cleavage of kininogen under formation of kallidin.