Oxidation-Reduction Properties of Chloroplast Thioredoxins, Ferredoxin:Thioredoxin Reductase, and Thioredoxin f-Regulated Enzymes

• Published in: Biochemistry (Easton) Vol. 38; no. 16; pp. 5200 - 5205
• Main Authors: Hirasawa, Masakazu, Schürmann, Peter, Jacquot, Jean-Pierre, Manieri, Wanda, Jacquot, Pierre, Keryer, Eliane, Hartman, Fred C, Knaff, David B
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 20.04.1999
• Subjects: Animals; Chlamydomonas reinhardtii; Chlamydomonas reinhardtii - metabolism; Chloroplast Thioredoxins; Chloroplasts - enzymology; Chloroplasts - metabolism; Enzyme Activation - drug effects; Ferredoxin-thioredoxin reductase; Freshwater; Fructose-Bisphosphatase - metabolism; Hydrogen-Ion Concentration; Iron-Sulfur Proteins; Oxidation-Reduction; Oxidoreductases - metabolism; Pisum sativum - enzymology; Pisum sativum - metabolism; Plant Proteins - metabolism; Plant Proteins - physiology; Spinacia oleracea - enzymology; Spinacia oleracea - metabolism; thioredoxin; Thioredoxins - pharmacology
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi982783v

Oxidation-reduction midpoint potentials were determined, as a function of pH, for the disulfide/dithiol couples of spinach and pea thioredoxins f, for spinach and Chlamydomonas reinhardtii thioredoxins m, for spinach ferredoxin:thioredoxin reductase (FTR), and for two enzymes regulated by thioredoxin f, spinach phosphoribulokinase (PRK) and the fructose-1,6-bisphosphatases (FBPase) from pea and spinach. Midpoint oxidation-reduction potential (E m) values at pH 7.0 of −290 mV for both spinach and pea thioredoxin f, −300 mV for both C. reinhardtii and spinach thioredoxin m, −320 mV for spinach FTR, −290 mV for spinach PRK, −315 mV for pea FBPase, and −330 mV for spinach FBPase were obtained. With the exception of spinach FBPase, titrations showed a single two-electron component at all pH values tested. Spinach FBPase exhibited a more complicated behavior, with a single two-electron component being observed at pH values ≥ 7.0, but with two components being present at pH values <7.0. The slopes of plots of E m versus pH were close to the −60 mV/pH unit value expected for a process that involves the uptake of two protons per two electrons (i.e., the reduction of a disulfide to two fully protonated thiols) for thioredoxins f and m, for FTR, and for pea FBPase. The slope of the E m versus pH profile for PRK shows three regions, consistent with the presence of pK a values for the two regulatory cysteines in the region between pH 7.5 and 9.0.