A Kazal-type serine proteinase inhibitor from chicken liver (clTI-1): Purification, primary structure, and inhibitory properties

Low-molecular-mass trypsin inhibitor (clTI-1; chicken liver Trypsin Inhibitor-1) was purified from chicken liver by extraction with perchloric acid, ammonium sulfate precipitation, a combination of ethanol-acetone fractionation followed by gel filtration, ion-exchange chromatography and RP-HPLC on a C18 column. The inhibitor occurs in two isoforms with molecular masses of 5938.56 and 6026.29 Da (determined by MALDI TOFF mass spectrometry). The complete amino acid sequences of both isoforms were determined (UniProtKB/Swiss-Prot P85000; ISK1L_CHICK). The inhibitor shows a high homology to Kazal-type family inhibitors, especially to trypsin/acrosin inhibitors and pancreatic secretory trypsin inhibitors. clTI-1 inhibits both bovine and porcine trypsin (Ka = 1.1 × 109 M−1 and 2.5 × 109 M−1, respectively). Significant differences were shown in the inhibition of the anionic and cationic forms of chicken trypsin (Ka = 4.5 × 108 M−1 and 1.2 × 1010 M−1). Weak interaction with human plasmin (Ka = 1.2 × 107 M−1) was also revealed.