title: Properties of purified cytosolic isoenzyme I of Cu,Zn-superoxide dismutase from Nicotiana plumbaginifolia leaves.
abstract: The isoenzyme I of cytosolic Cu,Zn-superoxide dismutase (SOD) from Nicotiana plumbaginifolia (tobacco) leaves has been purified to apparent homogeneity. The relative molecular mass of the native isoenzyme, determined by gel filtration chromatography, is about 33.2 kDa. SDS-polyacrylamide gel electrophoresis shows that the enzyme is composed of two equal subunits of 16.6 kDa The isolectric point, assayed by isoelectric focusing, in the pH range of 3.5-6.5, is 4.3. The enzyme stability was tested at different temperatures, pH, and concentration of inhibitors (KCN and H(2)O(2)). The catalytic constant (k(cat)) was 1.17 +/- 0.14 x 10(9) M(-1) s(-1) at pH 9.9 and 0.1 M ionic strength. The activation energy of the thermal denaturation process is 263 kJ mol(-1). The electrostatic surface potential of the modeled tobacco Cu,Zn-SOD I was calculated showing that the functional spatial network of charges on the protein surface has been maintained, independently of the amino acid substitution around the active sites.
authors.affiliation: Department of Chemical Sciences, University of Catania, 95125 Catania, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Ragusa
authors.forename: M T
authors.initials: MT
authors.lastname: Cambria
authors.forename: M
authors.initials: M
authors.lastname: Scarpa
authors.forename: M L
authors.initials: ML
authors.lastname: Di Paolo
authors.forename: M
authors.initials: M
authors.lastname: Falconi
authors.forename: A
authors.initials: A
authors.lastname: Rigo
authors.forename: A
authors.initials: A
authors.lastname: Cambria
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D003600:Cytosol / Q000201:enzymology; D004563:Electrochemistry; D004591:Electrophoresis, Polyacrylamide Gel; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004795:Enzyme Stability; D005459:Fluorides / Q000378:metabolism; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007526:Isoelectric Point; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D018515:Plant Leaves / Q000201:enzymology; D013482:Superoxide Dismutase / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D013499:Surface Properties; D014026:Nicotiana / Q000201:enzymology*
chemical_list: D004791:Enzyme Inhibitors; D007527:Isoenzymes; D013482:Superoxide Dismutase; D005459:Fluorides