title: A serine endopeptidase from cucumber leaves is inhibited by L-arginine, guanidino compounds and divalent cations.
abstract: An endopeptidase was purified and characterized from green leaves of cucumber (Cucumis sativus L. suyo). The purified enzyme, a basic amino acid-specific endopeptidase with a pI of 5.0, was a monomeric protein of 80 kDa whose pH optimum was 9.5. Inhibitor analysis suggested that it was a serine endopeptidase and contained sulfhydryl groups essential for catalytic activity. Analysis of internal amino acid sequences of the endopeptidase showed no significant similarity to other proteins. Its activity was inhibited by L-Arg and guanidino compounds having high hydrophobicity, as well as divalent cations such as Mg2+ and Ca2+. The K(i) values of L-Arg and Mg2+, which are also likely in vivo inhibitors, were 3.5 and 10 mM, respectively. Inhibition by L-Arg and Mg2+ was additive, and more than 70% of the activity was reversibly inhibited under their physiologically significant concentrations. These results suggest that the enzyme is possibly regulated by L-Arg and/or guanidino compounds, and by divalent cations in vivo.
authors.affiliation: Laboratory of Plant Biotechnology, Faculty of Agriculture, Tottori University, Koyama, 680-8553, Tottori, Japan. yamauchi@muses.tottori-u.ac.jp
authors.forename: Y
authors.initials: Y
authors.lastname: Yamauchi
authors.forename: T
authors.initials: T
authors.lastname: Sugimoto
authors.forename: K
authors.initials: K
authors.lastname: Sueyoshi
authors.forename: Y
authors.initials: Y
authors.lastname: Oji
authors.forename: K
authors.initials: K
authors.lastname: Tanaka
mesh_terms: D000376:Agmatine / Q000494:pharmacology; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology; D018553:Cucumis sativus / Q000201:enzymology*; D010450:Endopeptidases / Q000302:isolation & purification / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005033:Ethylmaleimide / Q000494:pharmacology; D005998:Glycine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D008274:Magnesium / Q000494:pharmacology; D018515:Plant Leaves / Q000201:enzymology; D012697:Serine Endopeptidases
chemical_list: D004791:Enzyme Inhibitors; D000376:Agmatine; D001120:Arginine; D010450:Endopeptidases; D012697:Serine Endopeptidases; C004946:glycocyamine; D008274:Magnesium; D005033:Ethylmaleimide; D002118:Calcium; D005998:Glycine