The Sulfite Oxidase of Thiobacillus ferrooxidans (Ferrobacillus ferrooxidans)

1971 ◽  
Vol 49 (10) ◽  
pp. 1125-1130 ◽  
Author(s):  
J. Robie Vestal ◽  
D. G. Lundgren

The sulfite oxidase (sulfite: cytochrome c oxidoreductase) from sulfur-grown Thiobacillus ferrooxidans was isolated and partially purified, and its properties were studied. The enzyme was purified 7.3-fold and was 75–85% of the protein present. Sulfite oxidase required SO32− for activity, and could use horse heart cytochrome c and ferricyanide as electron acceptors. The molecular weight was 41 500. The enzyme had a Km for sulfite of 0.58 mM with either ferricyanide or cytochrome c as the electron acceptor. The Km for ferricyanide was 0.25 mM. 5′-AMP did not stimulate enzyme activity. Other properties of the enzyme were similar to the enzyme from Thiobacillus thioparus and Thiobacillus novellus. A metabolic scheme of sulfur utilization for energy production in Thiobacillus ferrooxidans is presented.

1970 ◽  
Vol 48 (3) ◽  
pp. 334-343 ◽  
Author(s):  
Ronald M. Lyric ◽  
Isamu Suzuki

Enzymes concerned with the oxidation of thiosulfate were investigated in extracts of Thiobacillus thioparus. The organism possessed sulfite oxidase as well as adenosine-5′-phosphosulfate reductase and thiosulfate-oxidizing enzyme. Sulfite oxidase was purified 160-fold and the properties were studied. The enzyme had a molecular weight of 54 000 and one non-heme iron. The pH had a marked effect on reaction velocity and Km for sulfite, and the pK values for free enzyme and enzyme–sulfite complex were determined as 8.9 and 6.2, respectively. Chloride inhibition was noncompetitive and phosphate was uncompetitive with respect to sulfite. In many properties the T. thioparus enzyme was similar to the enzyme isolated from Thiobacillus novellus.


1991 ◽  
Vol 56 (2) ◽  
pp. 478-490 ◽  
Author(s):  
Joaquin F. Perez-Benito ◽  
Conchita Arias

The reaction between horse-heart cytochrome c and ascorbic acid has been investigated in the pH range 5.5 – 7.1 and at 10.0 – 25.0 °C. The rate shows a first-order dependence on the concentration of cytochrome c, it increases in a non-linear way as the concentration of ascorbic acid increases, it increases markedly with increasing pH and, provided that the ionic strength of the medium is high enough, it fulfills the Arrhenius equation. The apparent activation energy increases as the pH of the solution increases. The results have been explained by means of a mechanism that includes the existence of an equilibrium between two forms (acidic and basic) of oxidized cytochrome c: cyt-H+ -Fe3+ + OH- cyt -Fe3+ + H2O, whose equilibrium constant is (6.7 ± 1.4). 108 at 25.0 °C, the acidic form being more reducible than the basic one. It is suggested that there is a linkage of hydrogenascorbate ion to both forms of cytochrome c previous to the redox reactions. Two possibilities for the oxidant-reductant linkage (binding and adsorption) are discussed in detail.


ChemInform ◽  
2010 ◽  
Vol 23 (27) ◽  
pp. no-no
Author(s):  
C. DI BELLO ◽  
C. VITA ◽  
L. GOZZINI

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