Purification, inhibitory properties and amino acid sequence of a new serine proteinase inhibitor from white musterd (Sinapis alba L.) seed

A new serine proteinase inhibitor, mustard trypsin inhibitor 2 (MTI-2), has been isolated from white mustard (Sinapis alba L.) seed by affinity chromatography and reverse phase HPLC. The protein inhibits the catalytic activity of bovine β-trypsin and bovine α-chymotrypsin, with dissociation constants (Kd) of 1.6 × 10-10 M and 5.0 × 10-7 M, respectively, at pH 8.0 and 21°C, the stiochiometry of both proteinase-inhibitor complexes being 1:1. The amino acid sequence of MTI-2, which was determined following S-pyridylethylation, is comprised of 63 residues, corresponding to a molecular weight of about 7 kDa, and shows only extremely limited homology to other serine proteinase inhibitors.