Isolation and partial characterization of the trypsin inhibitor from the seeds of Brassica oleracea var. sabellica.

A trypsin inhibitor was extracted from the kale seeds with 0.01 M-HCl, precipitated with ammonium sulphate, and purified by affinity chromatography on immobilized trypsin and ion-exchange chromatography on QAE-Sephadex A-25. The inhibitor, of Mr 8 000, is composed of 64 amino acid residues and contains neither threonine nor methionine. Its isoelectric point is 8.9. In addition to trypsin, the inhibitor acts on subtilopeptidase A and shows a very weak antichymotrypsin activity. The factors modifying the arginine residues inactivate the inhibitor. A modified form of the inhibitor (with a broken reactive site peptide bond) has been isolated in pure form, and its properties were compared with those of the virgin form.