Nitrite Oxidoreductase in Nitrobacter

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Nitrite Oxidoreductase in Nitrobacter

• Whitney Hough
• CH 564
• 3-6-07

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Nitrobacter

• Gram negative
• Rod-shaped
• Obligate aerobe
• Cannot multiply or convert ammonia or nitrites in
  the absence of oxygen

Image http//www.princeton.edu/chm333/2004/Biore
mediation/images/nitrobacter.jpg
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Nitrite Oxidoreductase (NOR)

• Oxidizes nitrite to nitrate
• Electrons travel a very short transport chain
• Occurs because of the high potential of the
  NO3-/NO2- couple
• Enzyme consisting of two subunits
• Alpha (?) subunit molecular weight 115,000
• Beta (?) subunit molecular weight 65,000
• Cytochromes a1 and c1 are associated with NOR
• Cytochrome c1 has been described as the ?-subunit

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Reaction
Image http//www.chem.umass.edu/thompson/Courses
/BioStruct/Fall2001/presentations/SyedPeeran/React
ion1.gif
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Structure of NOR

• Catalytically active and includeds molybdenum and
  iron-sulfur clusters
• Genes have been identifed but only ?-subunit has
  been sequenced completely.
• Has been shown to be an electron-channeling
  protein
• Acting between the nitrite-oxidizing ?-subunit
  and the membrane-integrated electron transport
  chain

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Location of NOR

• Membrane bound
• inner side of the cytoplasmic
• ?-subunit is bound specifically to the membrane
• ? is bound at the periphery of the membrane
  fragments

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Picture of NOR
NOR particles of Nitrobacter negatively stained
with uranyl acetate. (A) Membrane-bound NOR
particles on the cytoplasmic side of a membrane
fragment. The arrowheads mark periodically
arranged particles in side view.
(B) Sequence of isolated NOR particles. Bar, 20 nm
E. Spieck et al, Journal of Structural Biology,
117, 117-123 (1996)