AMINO-ACID-SEQUENCE OF A BOWMAN-BIRK PROTEINASE-INHIBITOR FROM PEA-SEEDS

Trypsin inhibitors from winter pea seeds (c.v. Frilene) have been puri fied by ammonium sulfate precipitation, gel filtration, and anion and cation exchange chromatography and shown to consist of six protease in hibitors (PSTI I, II, III, IVa, IVb, and V). Their molecular weights w ere determined by electrospray mass spectrometry as 6916, 6807, 7676, 7944, 7848, and 7844 D, respectively, and the sequences of the first 2 0 N-terminal amino acid residues of these six inhibitors were found to be identical. The complete amino acid sequence of PSTI IVa was determ ined. This protein comprises a total of 72 residues and has 14 cystein es, all involved in disulfide bridges. Comparison of the sequence of P STI IVa with those of other leguminous Bowman-Birk type inhibitors rev ealed that PSTI could be classified as a group III inhibitor, closely related to Vicia faba and Vicia angustifolia inhibitors.