Purification and characterization of low molecular weight kininogen from pig plasma

A cysteine proteinase inhibitor from pig plasma with a molecular weight (MW ) of 55 kDa, purified to electrophoretical homogeneity, inhibited mu- and m -calpains, cathepsins B, L, and L-like, and papain, but did not inhibit try psin, beta-chymotrypsin, and cathepsin D. The purified inhibitor was stable at pH 3.0 to 10.5. The amounts for 50% inactivation (ID50) of papain, cath epsins B, L, and L-like, mu- and m-calpains were 10.55, 12.91, 2.18, 2.18, 30.91, and 29.27 nM, while the inhibition constant (K-i) for cathepsins B, L, L-like, and X, and mu- and m-calpains were 1.1, 0.64, 63.33, 8.19, 26, a nd 23.57 nM, respectively, It could inhibit the proteolysis of mackerel myo sin heavy chain caused by purified cathepsin L-like at 55 degrees C. Based on the MW, stability and specificity, it was identified as L-kininogen.