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Respiratory enzymes of Thiobacillus ferrooxidans. A kinetic study of electron transfer between iron and rusticyanin in sulfate media.

1987; Elsevier BV; Volume: 262; Issue: 31 Linguagem: Inglês

10.1016/s0021-9258(18)48126-4

1083-351X

Robert C. Blake, Elizabeth A. Shute,

Electrochemical Analysis and Applications

Thiobacillus ferrooxidans is a chemolithotrophic bacterium capable of fulfilling all of its energy requirements from the oxidation of soluble ferrous sulfate.Rusticyanin is a soluble blue copper protein found in abundance in the periplasmic space of this bacterium.The one-electron transfer reaction between soluble iron and purified rusticyanin has been studied by stopped flow spectrophotometry in acidic solutions containing sulfate.Second order rate constants for the reduction of rusticyanin by Fez+, FeHSO:, and FeS09 were 0.022, 0.73, and 2.30 M-' s-', respectively.The pseudo-first order rate constant for the reduction of rusticyanin exhibited substrate saturation when the concentration of the total ferrous ion was varied in solutions of limiting sulfate.This saturation behavior was quantitatively described using the values of the second order rate constants listed above and the distribution of the total ferrous ion into its water-, bisulfate-, and sulfate-coordinated forms.Second order rate constants for the oxidation of rusticyanin by Fe3+ and FeSO: were 0.73 and 0.26 M-' s-', respectively.The electron transfer reactions between iron and rusticyanin monitored in vitro were far too slow to support the hypothesis that rusticyanin is the primary oxidant of ferrous ions in the iron-dependent respiratory electron transport chain of T. ferrooxidans.Thiobacillus ferrooxidans is the most extensively characterized member of a group of chemolithotrophic bacteria that inhabit ore-bearing geological formations exposed to the atmosphere and obtain all of their energy for growth from the dissolution and oxidation of minerals within the ore.These Gram-negative, obligately acidophilic bacteria display optimal growth from pH 1.5 to 3.5 (2-4).T. ferrooxidans takes its species name from its ability, unique among the thiobacilli, to grow in the laboratory using soluble ferrous sulfate as its sole source of energy (5-7).Energy is derived from oxidative phosphorylation coupled to respiratory electron transfer; molecular oxygen is the ultimate electron acceptor.Cytochromes c and a have been identified in T. ferrooxidans, and numerous reports have demonstrated that both types of cytochromes are reduced in intact cells exposed to Fe(I1) (8-11).Contrary to earlier reports of a cytoplasmic iron-cytochrome c reductase (12-14), it is now generally accepted that