Spectroscopic studies of the tungsten-containing formaldehyde ferredoxin oxidoreductase from the hyperthermophilic archaeon Thermococcus litoralis.

摘要: The electronic and redox properties of the iron-sulfur cluster tungsten center in as-isolated sulfide-activated forms formaldehyde ferredoxin oxidoreductase (FOR) from Thermococcus litoralis (Tl) have been investigated by using combination EPR variable-temperature magnetic circular dichroism (VTMCD) spectroscopies. results reveal a [Fe4S4]2+,+ (Em=-368mV) that undergoes cycling between an oxidized form with S=0 ground state reduced exists as pH- medium-dependent mixture S=3/2 (g=5.4; E/D=0.33) S=1/2 (g=2.03, 1.93, 1.86) states, former dominating presence 50% (v/v) glycerol. Three distinct types W(V) signals observed during dye-mediated titration Tl FOR. initial resonance upon oxidation, termed "low-potential" species (g=1.977, 1.898, 1.843), corresponds to approximately 25-30% total W W(IV)/ W(V)/W(VI) states at physiologically relevant potentials (Em= -335 -280 mV, respectively). At higher minor "mid-potential" species, g= 1.983, 1.956, 1.932, accounting for less than 5 % W, appears midpoint potential -34 mV persists up least + 300 mV. above 0 major "high-potential" signal, 1.981, 1.883, 30-40% +184 As-isolated samples FOR were found undergo 8-fold enhancement activity on incubation excess Na2S under reducing conditions was partially inactivated cyanide. spectroscopic are quite those enzyme, loss low-potential changes both mid-potential (g= 1.950, 1.931; Em = -265 mV) high-potential (g=1.981, 1.952, 1.895; +65 mV). Taken together, maximally account only 15% W. Both lost cyanide is converted into exposure air. Structural models proposed each be artifacts ligand-based oxidation W(VI) species. A terminal sulfido or thiol ligands responsible catalytic