AMINO-ACID-SEQUENCES OF TRYPSIN-INHIBITORS FROM THE MELON CUCUMIS-MELO

Two squash family trypsin inhibitors, CMeTI-A and CMeTI-B, were isolat ed from the melon (Cucumis melo) seeds, by ion exchange chromatography , gel filtration, affinity chromatography, and high-performance liquid chromatography, and their amino acid sequences were determined. All i nhibitors contain 29 amino acid residues including 6 half-cystine resi dues. They differ by twelve amino acid residues. These polypeptides ar e strong inhibitors of bovine trypsin, with K-i values of 1.6 X 10(-10 ) M (CMeTI-A) and 4.7 X 10(-10) M (CMeTI-B). The products of CMeTI-A a nd CMeTI-B cleaved at their reactive sites by tryptic digestion during the purification by trypsin-Sepharose 4B affinity column chromatograp hy are active against trypsin activity, but a molar ratio of inhibitor to trypsin of 2:1 for trypsin-treated CMeTI-B or 1:1 for trypsin-trea ted CMeTI-A is required.