title: The oxidation-reduction properties of spinach thioredoxins f and m and of ferredoxin:thioredoxin reductase.
abstract: Oxidation-reduction midpoint potentials have been determined, using cyclic voltammetry, for the active-site disulfide/dithiol couples of spinach thioredoxins f and m and of spinach ferredoxin:thioredoxin reductase (FTR) and for a component likely to be the [4Fe-4S] cluster of FTR. Values for the midpoint potentials (n = 2) of -210 +/- 10 mV were determined for both thioredoxins f and m. Two redox centers were detected in FTR, with midpoint potential values of -230 +/- 10 mV (n = 2) and +340 +/- 30 mV, respectively. Alkylation of the active-site cysteines of FTR by treatment of the enzyme with N-ethylmaleimide (NEM) eliminates the component with the -230 mV midpoint potential, allowing one to assign this value to the active site disulfide/dithiol couple. Inasmuch as the only other electron-carrying center known to be present in FTR is the [4Fe-4S] cluster, it appears likely that the high-potential component can be attributed to this redox moiety. The midpoint potential value of the high-potential feature shifts slightly, to +380 +/- 20 mV, in the NEM-treated enzyme.
authors.affiliation: Department of Biochemistry, University of Arizona, Tucson 85721, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Salamon
authors.forename: G
authors.initials: G
authors.lastname: Tollin
authors.forename: M
authors.initials: M
authors.lastname: Hirasawa
authors.forename: L
authors.initials: L
authors.lastname: Gardet-Salvi
authors.forename: A L
authors.initials: AL
authors.lastname: Stritt-Etter
authors.forename: D B
authors.initials: DB
authors.lastname: Knaff
authors.forename: P
authors.initials: P
authors.lastname: Schürmann
mesh_terms: D054479:Chloroplast Thioredoxins; D005033:Ethylmaleimide / Q000494:pharmacology; D005288:Ferredoxins / Q000378:metabolism*; D007506:Iron-Sulfur Proteins; D008051:Lipid Bilayers; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000187:drug effects / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism*; D011199:Potentiometry; D018724:Spinacia oleracea; D013879:Thioredoxins / Q000378:metabolism*
chemical_list: D054479:Chloroplast Thioredoxins; D005288:Ferredoxins; D007506:Iron-Sulfur Proteins; D008051:Lipid Bilayers; D010940:Plant Proteins; D013879:Thioredoxins; D010088:Oxidoreductases; C021588:ferredoxin-thioredoxin reductase; D005033:Ethylmaleimide