Oxidation-Reduction Properties of Flavodoxin from Peptostreptococcus elsdenii
Year: 1969
Type: article
Abstract: Peptostreptococcus elsdenii flavodoxin is completely reduced by 1 mole of sodium dithionite per mole of proteinbound flavin mononucleotide; 0.5 mole of dithionite generates almost maximum flavin semiquinone. The amount of semiquinone formed is dependent on pH. Semiquinone formation constants determined at pH 8.3 and 9.26, were 910 and 110, respectively. Fully reduced flavodoxin reacts rapidly with oxidized flavodoxin to form semiquinone. The rate of this reaction is pH-dependent and decreases from 105 m-1 min-1 at pH 6.7 to 1.6 x 104 m-1 min-1 at pH 9.26. The oxidation-reduction potential (E2) for the couple oxidized flavodoxin/flavodoxin semiquinone was determined by equilibrium experiments with indigo dyes. E2 was -0.115 volt at pH 7. The oxidation-reduction potential (E1) for the couple semiquinone/fully reduced flavodoxin was determined from the equilibrium concentration of these components after treating flavodoxin with hydrogen and hydrogenase. E1 was -0.373 volt at pH 7. A value for E1 was also obtained from the concentrations of fully reduced flavodoxin and flavodoxin semiquinone formed in equilibrium with excess TPNH in the presence of spinach ferredoxin-TPN reductase. By this method E1 was -0.371 volt at pH 7. The effect of pH on E1 suggests an ionization in fully reduced flavodoxin with a pK = 5.8. When reduced flavodoxin is mixed with air, the semiquinone is formed rapidly. Air oxidation of flavodoxin semiquinone is slow; the observed rate is markedly dependent on pH.
Source: Journal of Biological Chemistry
Authors: S G Mayhew, G P Foust, V Massey
Institution: University of Michigan
Language: English
Field: Energy
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $3,430
OpenAlex ID: W1594630507