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Nitrite Reductases

Different Types of Nitrite Reductases. 3 Periplasmic ReductasesCytochrome c Respiratory Nitrite ReductaseCytochrome cd1 Nitrite ReductaseCopper Nitrite Reductase1 Cytoplasmic ReductaseNADH-dependent Siroheme Nitrite Reductase. Two types of Heme's in Cytochrome cd1. Cytochrome c . Cytochrome d1

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Nitrite Reductases

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    1. Nitrite Reductases A foray into the many types, functions, and intermediates of Nitrite Reductases

    2. Different Types of Nitrite Reductases 3 Periplasmic Reductases Cytochrome c Respiratory Nitrite Reductase Cytochrome cd1 Nitrite Reductase Copper Nitrite Reductase 1 Cytoplasmic Reductase NADH-dependent Siroheme Nitrite Reductase

    3. Two types of Hemes in Cytochrome cd1 Cytochrome c Cytochrome d1

    4. Cytochrome cd1 Found in Paracoccus and Pseudomonas Heterodimer Each monomer composed of two domains Cyt c covalently bound to smaller domain Cyt d1 noncovalently bound to 8 bladed -propeller

    6. Cytochrome cd1 Reduces NO2- ? NO

    7. Copper Nitrite Reductase Found in Pseudomonas Homotrimer Each monomer forms two barrel domains Each enzyme contains six Copper Centers 3 Type I 3 Type II

    8. Copper Nitrite Reductase Electrons donated from donor proteins to Type I center Electrons come from cupredoxins and cytochromes Type I center donates electrons to Type II center Type II center = site of catalytic activity

    9. Copper Nitrite Reductase Uses a Copper (I) cation bound to the enzyme to bind NO2- Produces nitric oxide (NO) in the presence of Nitrite ions (NO2-)

    10. Copper Nitrite Reductase However, in the presence of both Nitric Oxide (NO) and of Nitrite ions (NO2-), the enzyme further reduces nitrogen to Nitrous Oxide (N2O).

    11. Less Useful Reductases Cytochrome c Respiratory Reductase Does not contribute to denitrification Overall Reaction: NO2- ? NH3 NO2- ? NO+ ? NOH ? NH2OH ? NH3

    12. Less Useful Reductases NADH-Dependent Siroheme Nitrite Reductase Unlike the other three, this one is found in the cytoplasm Most likely serves to remove NO2- from the cell (toxic at high levels) NO2- ? NH4+

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