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- Title
Unexpected weak magnetic exchange coupling between haem and non-haem iron in the catalytic site of nitric oxide reductase (NorBC) from Paracoccus denitrificans.
- Authors
VAN WONDEREN, Jessica H.; OGANESYAN, Vasily S.; WATMOUGH, Nicholas J.; RICHARDSON, David J.; THOMSON, Andrew J.; CHEESMAN, Myles R.
- Abstract
Bacterial NOR (nitric oxide reductase) is a major source of the powerful greenhouse gas N2O. NorBC from Paracoccus denitrificans is a heterodimeric multi-haem transmembrane complex. The active site, in NorB, comprises high-spin haem b3 in close proximity with non-haem iron, FeB. In oxidized NorBC, the active site is EPR-silent owing to exchange coupling between FeIII haem b3 and FeB III (both S=5/2).On the basis of resonanceRaman studies [Moenne-Loccoz, Richter, Huang,Wasser, Ghiladi,Karlin and de Vries (2000) J. Am. Chem. Soc. 122, 9344-9345], it has been assumed that the coupling is mediated by an oxo-bridge and subsequent studies have been interpreted on the basis of this model. In the present study we report a VFVT (variablefield variable-temperature) MCD (magnetic circular dichroism) study that determines an isotropic value of J= -1.7 cm-1 (H = -J S1 · S2) for the coupling. This is two orders of magnitude smaller than that encountered for oxo-bridged diferric systems, thus ruling out this configuration. Instead, it is proposed that weak coupling is mediated by a conserved glutamate residue.
- Subjects
NITRIC oxide; REDUCTASES; GREENHOUSE gases; PARACOCCUS denitrificans; MEMBRANE proteins; GLUTAMIC acid
- Publication
Biochemical Journal, 2013, Vol 451, Issue 3, p389
- ISSN
0264-6021
- Publication type
Article
- DOI
10.1042/BJ20121406