Spectroscopic studies of ferricyanide oxidation of Azotobacter vinelandii ferredoxin I.

AUTOR(ES)

Morgan, T V

RESUMO

The Fe(CN)3-(6) oxidation of the crystallographically characterized [[3Fe-3S], [4Fe-4S]] ferredoxin I of Azotobacter vinelandii has been studied using absorption, circular dichroism, magnetic circular dichroism, and EPR spectroscopies. A paramagnetic intermediate is observed en route to Fe-S cluster-free apoprotein, possessing an anisotropic g approximately equal to 2 EPR signal, surviving to temperatures greater than 77 K. This species is shown to result from 3-electron oxidation of the [4Fe-4S] cluster, without modification of the [3Fe-3S] cluster. However, it does not give rise to observable paramagnetic magnetic circular dichroism in the visible-near UV spectral region and is therefore neither an oxidized HIPIP [4Fe-4S] cluster nor an oxidized [3Fe-3S] cluster. We identify the paramagnetic species as a cysteinyldisulfide radical formed on dissociation of an oxidized cysteinate and an oxidized sulfide ion from the [4Fe-4S] cluster. This conclusion is consistent with the observed reaction stoichiometry, the spectroscopic results obtained, known EPR spectra of disulfide radicals, and the reconstitution of the native [4Fe-4S] cluster by dithiothreitol alone. This reaction, earlier interpreted as a HIPIP-type oxidation, is a previously uncharacterized oxidation reaction of [4Fe-4S] clusters.

Documentos Relacionados

• Structure of ferredoxin I from Azotobacter vinelandii.
• Potentiometric titration of the high- and low-potential 4Fe-4S* centers of Azotobacter vinelandii ferredoxin I.
• Construction and characterization of an Azotobacter vinelandii strain with mutations in the genes encoding flavodoxin and ferredoxin I.
• RIBONUCLEIC ACID POLYMERASE OF AZOTOBACTER VINELANDII, I. PRIMING BY POLYRIBONUCLEOTIDES*
• Site-directed mutagenesis of Azotobacter vinelandii ferredoxin I: [Fe-S] cluster-driven protein rearrangement.