title: Effect of pH on the oxidation-reduction properties of thioredoxins.
abstract: Oxidation-reduction midpoint potential (E(m)) versus pH profiles were measured for wild-type thioredoxins from Escherichia coli and from the green alga Chlamydomonas reinhardtii and for a number of site-directed mutants of these two thioredoxins. These profiles all exhibit slopes of approximately -59 mV per pH unit, characteristic of the uptake of two protons per reduction of an active-site thioredoxin disulfide, at acidic, neutral, and moderately alkaline pH values. At higher pH values, these profiles exhibit slopes of either -29.5 mV per pH unit, characteristic of the uptake of one proton per disulfide reduced, or are pH-independent, indicating that neither proton uptake nor proton release is associated with reduction of the active-site disulfide. Reduction of the two wild-type thioredoxins is accompanied by the uptake of two protons even at pH values where the more acidic cysteine thiol group of the reduced proteins would be expected to be completely unprotonated. The effect of site-directed mutagenesis of two highly conserved aspartate residues that play important structural and/or catalytic roles in both thioredoxins, and which could in principle play a role in proton transfer, on the pK(a) values of redox-linked acid dissociations (deduced from changes in slope of the E(m) versus pH profiles) has also been determined for both E. coli thioredoxin and C. reinhardtii thioredoxin h.
authors.affiliation: Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79401-1061, USA.
authors.forename: Aaron T
authors.initials: AT
authors.lastname: Setterdahl
authors.forename: Peter T
authors.initials: PT
authors.lastname: Chivers
authors.forename: Masakazu
authors.initials: M
authors.lastname: Hirasawa
authors.forename: Stéphane D
authors.initials: SD
authors.lastname: Lemaire
authors.forename: Eliane
authors.initials: E
authors.lastname: Keryer
authors.forename: Myroslawa
authors.initials: M
authors.lastname: Miginiac-Maslow
authors.forename: Sung-Kun
authors.initials: SK
authors.lastname: Kim
authors.forename: Jeremy
authors.initials: J
authors.lastname: Mason
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Jacquot
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Longbine
authors.forename: Frédéric
authors.initials: F
authors.lastname: de Lamotte-Guery
authors.forename: David B
authors.initials: DB
authors.lastname: Knaff
mesh_terms: D000409:Alanine / Q000235:genetics; D000818:Animals; D001224:Aspartic Acid / Q000235:genetics; D001665:Binding Sites / Q000235:genetics; D016825:Chlamydomonas reinhardtii / Q000737:chemistry* / Q000235:genetics; D003545:Cysteine / Q000737:chemistry / Q000235:genetics; D004220:Disulfides / Q000737:chemistry; D004579:Electron Transport / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D011522:Protons; D054480:Thioredoxin h; D013879:Thioredoxins / Q000737:chemistry* / Q000235:genetics; D014364:Tryptophan / Q000235:genetics
chemical_list: D004220:Disulfides; D029968:Escherichia coli Proteins; D011522:Protons; D054480:Thioredoxin h; D001224:Aspartic Acid; D013879:Thioredoxins; D014364:Tryptophan; D003545:Cysteine; D000409:Alanine