Nitrate reductase localization

Two types of dissimilatory nitrate reductases, localized in either the cytoplasmic membrane or the periplasm, are widespread among bacteria. The cytoplasmic membrane-bound nitrate reductase (Nar) catalyzes the first steps of denitrification (NOs" N02 NO N2O... 

Two types of dissimilatory nitrate reductases, localized in either the cytoplasmic membrane or the periplasm, are widespread among bacteriaT" The cytoplasmic membrane-bound nitrate reductase (Nar) catalyzes the first steps of denitrification (NOs N02 NO N2O N2) and nitrate ammonification (NOs"N02 NH3). These reactions are the terminal electron-transfer reactions during anaerobic respiration, the enzymes being part of a redox loop generating a proton-motive force capable of driving ATP synthesis.Periplasmic nitrate reductase (Nap) participates in cellular redox processes, aerobic denitrification, and nitrate scavenging. ... 

The organization of the enzymes of denitrification in gram-negative bacteria, as determined by antibody labelling and electron microscopy studies, is shown in Figure 5. The first enzyme, nitrate reductase (NaR), resides in the cytoplasmic membrane with its active site accessed from the cytoplasmic side, necessitating transport of nitrate across both the periplasmic and cytoplasmic membranes. The product nitrite is transported back into the periplasmic space, where it is reduced by the nitrite reductase (NiR). Most NiR s appear to be soluble enzymes, although there have been reports of preparations in which the activity was associated with membrane fractions. The nitric oxide reductase (NoR) is also localized in the cytoplasmic membrane, and releases its product N2O back into the cytoplasmic space, where the soluble enzyme nitrous oxide reductase (NoS) converts it to N2. 

In C4 plants, nitrate and nitrite reductases, especially the former, were localized primarily in the mesophyll leaf cells, although some nitrite reductase was found in the bundle sheath cells (Mellor and Treguna, 1971 Rathnam and Edwards, 1976 Hard et al., 1977 Neyra and Hageman, 1978). 

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