Abstract
The dissimilatory nitrite reductase from Desulfovibrio desulfuricans ATCC 27774 catalyzes the reduction of nitrite to ammonia. Previous spectroscopic investigation revealed that it is a hexaheme cytochrome containing one high spin ferric heme and five low spin ferric hemes in the oxidized enzyme. The current study uses the high resolution of Mössbauer spectroscopy to obtain redox properties of the six heme groups. Correlating the Mössbauer findings with the EPR data reveals the pairwise spin-spin coupling among four of the heme groups. The other two hemes are found to be magnetically isolated. Reduction with dithionite and reaction with CO further indicate that only the high spin heme is capable of binding small exogenous ligands. These results confirm our previous finding that Desulfovibrio desulfuricans nitrite reductase contains six heme groups and that the high spin ferric heme is the substrate and inhibitor binding site.
Highlights
The dissimilatory reduction of nitrite to ammonia is a common occurrence in microorganisms
At pH 7.6, the as-isolated D. desulfuricans nitrite reductase exhibits a complex EPR spectrum consisting of a low spin ferric heme signal at g ϭ 2.96, 2.28, and 1.50 with additional broad resonances at several low field regions (g ϭ 3.92 and 4.8), indicative of spin-spin interaction
We report a detailed redox titration study of the D. desulfuricans nitrite reductase monitored by Mossbauer spectroscopy
Summary
The dissimilatory reduction of nitrite to ammonia is a common occurrence in microorganisms. At pH 7.6, the as-isolated D. desulfuricans nitrite reductase exhibits a complex EPR spectrum consisting of a low spin ferric heme signal at g ϭ 2.96, 2.28, and 1.50 with additional broad resonances at several low field regions (g ϭ 3.92 and 4.8), indicative of spin-spin interaction
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