PREPARATION AND CHARACTERISTICS OF TRYPSIN-INHIBITORS FROM THE SEEDS OF SQUASH (CUCURBITA-MAXIMA) AND ZUCCHINI (CUCURBITA-PEPO-VAR-GIROMONTIA)

  • 1 January 1983
    • journal article
    • research article
    • Vol. 30  (2) , 127-+
Abstract
One trypsin inhibitor (I) from zucchini seeds and 2 (I and III) from squash seeds were isolated by ammonium sulfate salting out and chromatography on SP-Sephadex C-25 and immobilized trypsin. The inhibitors have the same molecular mass, about 3300, contain 29 amino acids have 3 disulfide bridges, and lack Thr, Phe and Trp. The isoelectric point of the zucchini inhibitor I and squash inhibitor I is 5.6, whereas that of the squash inhibitor III, is 8.3. Arg is the N-terminal amino acid of all 3 inhibitors. On modification of the Arg residues with 1,2-cyclohexanedione both squash inhibitors become inactivated. Zucchini inhibitor I becomes inactivated on acetylation of free amino groups. In all 3 inhibitors, on enzymatic modification with trypsin at pH 3.2, Ile appears as a new N-terminal amino acid. On this basis it can be supposed that Arg-Ile form the reactive site of the trypsin inhibitors from squash seeds, and Lys-Ile of the zucchini seed inhibitor.