Correlation of optical and EPR signals with the P460 heme of hydroxylamine oxidoreductase from Nitrosomonas europaea

Biochemistry
D M ArcieroA B Hooper

Abstract

Hydroxylamine oxidoreductase (HAO) of Nitrosomonas europaea catalyzes the four-electron oxidation of NH2OH to NO2-. Each subunit of the trimeric enzyme contains seven c-hemes and one heme P460. In previous work [Hendrich, M. P., et al. (1994) J. Am. Chem. Soc. 116, 11961-11968], an integer-spin EPR signal at g = 7.7 was discovered from the active site of the resting enzyme. This new signal was assigned to an exchange-coupled cluster containing ferric heme P460 and a ferric c-heme. An electrochemical titration of HAO is presented here in which EPR signals and optical bands, believed to be associated with the P460 heme, are monitored. In the EPR titration, as a redox center with Em8 = -140 mV becomes reduced, the integer-spin signal disappears. Then, upon reduction of a redox center with Em8 = -190 mV, a g = 6 type signal, which has been previously assigned to a high-spin form of the ferric P460 heme of HAO, appears. However, in the -140 to -190 mV range, we have been unable to identify an additional EPR signal attributable to the P460 center. Thus, the electronic environment of oxidized P460 heme of HAO appears to pass through three states before reduction in a titration experiment, with an intermediate state that is not readily...Continue Reading

References

Aug 17, 1972·Biochimica Et Biophysica Acta·R H Erickson, A B Hooper

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Citations

Mar 30, 2006·Journal of the American Chemical Society·Anup K UpadhyayMichael P Hendrich
May 29, 1999·Current Opinion in Chemical Biology·D J Richardson, N J Watmough
Mar 14, 2008·Journal of Inorganic Biochemistry·M Laura FernándezSara E Bari
Jun 19, 2016·The Journal of Biological Chemistry·Wouter J MaalckeBoran Kartal
Oct 11, 2003·FEMS Microbiology Reviews·Ingo SchmidtMarc Strous
Apr 16, 2003·Inorganic Chemistry·Maria Zulema Cabail, A Andrew Pacheco
Jul 18, 2001·Journal of the American Chemical Society·M P HendrichA B Hooper

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