title: Purification, amino acid sequence, and cDNA cloning of trypsin inhibitors from onion (Allium cepa L.) bulbs.
abstract: Three protease inhibitors (OTI-1-3) have been purified from onion (Allium cepa L.) bulbs. Molecular masses of these inhibitors were found to be 7,370.2, 7,472.2, and 7,642.6 Da by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), respectively. Based on amino acid composition and N-terminal sequence, OTI-1 and -2 are the N-terminal truncated proteins of OTI-3. All the inhibitors are stable to heat and extreme pH. OTI-3 inhibited trypsin, chymotrypsin, and plasmin with dissociation constants of 1.3 x 10(-9) M, 2.3 x 10(-7) M, and 3.1 x 10(-7) M, respectively. The complete amino acid sequence of OTI-3 showed a significant homology to Bowman-Birk family inhibitors, and the first reactive site (P1) was found to be Arg17 by limited proteolysis by trypsin. The second reactive site (P1) was estimated to be Leu46, that may inhibit chymotrypsin. OTI-3 lacks an S-S bond near the second reactive site, resulting in a low affinity for the enzyme. The sequence of OTI-3 was also ascertained by the nucleotide sequence of a cDNA clone encoding a 101-residue precursor of the onion inhibitor.
authors.affiliation: Department of Chemistry, Faculty of Science, Fukuoka University, 8-19-1 Nanakuma, Jonan-ku, Fukuoka 814-0180, Japan.
authors.forename: Masanobu
authors.initials: M
authors.lastname: Deshimaru
authors.forename: Akira
authors.initials: A
authors.lastname: Watanabe
authors.forename: Keiko
authors.initials: K
authors.lastname: Suematsu
authors.forename: Maki
authors.initials: M
authors.lastname: Hatano
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Terada
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D001483:Base Sequence; D002852:Chromatography, Ion Exchange; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D004355:Drug Stability; D005341:Fibrinolysin / Q000037:antagonists & inhibitors; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D019697:Onions / Q000737:chemistry* / Q000235:genetics; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013696:Temperature; D014358:Trypsin Inhibitor, Bowman-Birk Soybean / Q000235:genetics; D014361:Trypsin Inhibitors / Q000737:chemistry* / Q000235:genetics* / Q000302:isolation & purification / Q000494:pharmacology
chemical_list: D000596:Amino Acids; D018076:DNA, Complementary; D014358:Trypsin Inhibitor, Bowman-Birk Soybean; D014361:Trypsin Inhibitors; D005341:Fibrinolysin