Effect of divers anions on the electron-transfer reaction between iron and rusticyanin from Thiobacillus ferrooxidans.
Rusticyanin is a soluble blue copper protein found in abundance in the periplasmic space of Thiobacillus ferrooxidans, an acidophilic bacterium capable of growing chemolithotrophically on soluble ferrous sulfate. The one-electron-transfer reactions between soluble iron and purified rusticyanin were studied by stopped-flow spectrophotometry in acidic solutions containing each of 14 different anions. The second-order rate constants for both the Fe(II)-dependent reduction and the Fe(III)-dependent oxidation of the rusticyanin varied as a function of the identity of the principal anion in solution. Analogous electron-transfer reactions between soluble iron and bis(dipicolinato)cobaltate(III) or bis(dipicolinato)ferrate(II) were studied by stopped-flow spectrophotometry under solution conditions identical with those of the rusticyanin experiments. Similar anion-dependent reactivity patterns were obtained with soluble iron whether the other reaction partner was rusticyanin or either of the two organometallic complexes. The Marcus theory of outer-sphere electron transfer reactions was applied to this set of kinetic data to demonstrate that the rusticyanin may possess at least two electron-transfer pathways for liganded iron, one where the pattern of electron-transfer reactivity is controlled largely by protein-independent activation parameters and one where the protein exhibits an anion-dependent kinetic specificity. The exact role of rusticyanin in the iron-dependent respiratory electron transport chain of T. ferrooxidans remains unclear.
Blake
R C
RC
Department of Biochemistry, Meharry Medical College, Nashville, Tennessee 37208.
White
K J
KJ
Shute
E A
EA
D000838:Anions / Q000737:chemistry; D001400:Azurin / Q000031:analogs & derivatives* / Q000737:chemistry; D001426:Bacterial Proteins / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D008024:Ligands; D010084:Oxidation-Reduction; D013816:Thermodynamics; D013855:Thiobacillus / Q000378:metabolism*
D000838:Anions; D001426:Bacterial Proteins; D008024:Ligands; C012543:rusticyanin; D001400:Azurin; D007501:Iron