title: Proteinaceous inhibitor versus fructose as modulators of Pteris deflexa invertase activity.
abstract: An acid invertase from the fern Pteris deflexa Link was purified and the effect of reaction products on enzyme activity was studied. Fructose and glucose were competitive and non-competitive inhibitors of the enzyme, respectively. Since proteins suppressed glucose and fructose inhibition of the enzyme, an invertase modulation by reaction products is unlikely; nevertheless, an invertase proteinaceous inhibitor previously reported could have a role in this respect. The purified enzyme was an heterodimer Mr 90,000 Daltons composed of subunits of 66,000 and 30,000 Daltons. The enzyme had beta-fructofuranosidase activity and hydrolyzed mainly sucrose but also raffinose and stachyose, with Km of 3.22, 10.80 and 38.50 mM, respectively. Invertase activity with an optimum pH at 5.0 was present in almost every leaf fern tissue. Pinnas (sporophyll leaflets) had the higher enzyme levels. Invertase histochemical and immunochemical localization studies showed the enzyme mainly in phloem cells. Epidermis, collenchyma and parenchyma cells also showed invertase protein.
authors.affiliation: Instituto de Estudios Vegetales Dr Antonio R. Sampietro, Facultad de Bioquímica, Química y Farmacia, Universidad Nacional de Tucumán, San Miguel de Tucumán, Argentina.
authors.forename: J E
authors.initials: JE
authors.lastname: Sayago
authors.forename: M A
authors.initials: MA
authors.lastname: Vattuone
authors.forename: A R
authors.initials: AR
authors.lastname: Sampietro
authors.forename: M I
authors.initials: MI
authors.lastname: Isla
mesh_terms: D004791:Enzyme Inhibitors / Q000737:chemistry* / Q000494:pharmacology; D005632:Fructose / Q000494:pharmacology*; D006026:Glycoside Hydrolases / Q000037:antagonists & inhibitors* / Q000302:isolation & purification; D007700:Kinetics; D010940:Plant Proteins / Q000737:chemistry* / Q000494:pharmacology*; D032495:Pteris / Q000201:enzymology*; D013379:Substrate Specificity; D043324:beta-Fructofuranosidase
chemical_list: D004791:Enzyme Inhibitors; D010940:Plant Proteins; D005632:Fructose; D006026:Glycoside Hydrolases; D043324:beta-Fructofuranosidase