Tissue kallikrein processes small proenkephalin peptides

Abstract Tissue kallikrein may play a role in processing precursor polypeptide hormones. We investigated whether hydrolysis of natural enkephalin precursors, peptide F and bovine adrenal medulla docosapeptide (BAM-22P), by hog pancreatic kallikrein is consistent with this concept. Incubation of peptide F with this tissue kallikrein resulted in the release of Met 5 -enkephalin and Met 5 -Lys 6 -enkephalin. Met 5 -Lys 6 -enkephalin was the main peptide released, indicating that the major cleavage site was between two lysine residues. At 37°C and pH 8.5, the K M values for formation of Met 5 -enkephalin and Met 5 -Lys 6 -enkephalin were 129 and 191 μM, respectively. Corresponding k cat values were 0.001 and 0.03 s −1 and k cat / K M ratios were 8 and 1.6·10 2 M −1 · s −1 , respectively. Cleavage of peptide F at acidic pH (5.5) was negligible. When BAM-22P was used as a substrate, Met 5 -Arg 6 -enkephalin was released, thus indicating cleavage between two arginine residues. At pH 8.5, K M was 64 μM, k cat was 4.5 s −1 , and the k cat / K M ratio was 7 · 10 4 M −1 · s −1 . At 5.5, the pH of the secretory granules, K M , k cat and k cat / K M were 184 μM, 1.9 s −1 and 10 4 M −1 · s −1 , respectively. It is unlikely that peptide F could be a substrate for kallikrein in vivo; however, tissue kallikrein could aid in processing proenkephalin precursors such as BAM-22P by cleaving Arg-Arg peptide bonds.