Nitrite reductase distribution

Coyne, M. S., Arunakumari, A., Averill, B. A., and Tiedje, J. M. (1989). Immunological identification and distribution of dissimilatory heme cd, and nonheme copper nitrite reductases in denitrifying bacteria. Appl. Environ. Microbiol. 55, 2924-2931. 

In various species of bacteria several different types of non-assimilatory nitrite reductases are found. Escherichia coli has a cytoplasmic NAD(P)H-dependent enzyme whose role seems to be detoxification of nitrite. This type of enzyme, coded for by the nirB gene, also contains siroheme as the redox active catalytic center (Cole, 1988). Additionally in E. coli, and expressed under different conditions to the cytoplasmic enzyme, is a periplasmic nitrite reductase that catalyses formation of ammonia from nitrite (Cole, 1988). This enzyme has five c-type (Figure 1) hemes per polypeptide chain one of these hemes, the catalytic site, has the unique CXXCK sequence as its attachment site (Einsle et al., 1999). Electrons reach this type of nitrite reductase, which is fairly widely distributed amongst the microbial world, from the cytoplasmic membrane electron transfer chain. The exact electron donor partner from such chains for this type of nitrite reductase is unknown (Berks et al., 1995). 

A literature search revealed that the distribution of the enzymes of nitrate assimilation had been determined in one case and was apparently as predicted by the theory. Nitrate and nitrite reductases were shown by isolation of mesophyll and bundle-sheath protoplasts to be predominantly in mesophyll cells. In addition, the enzymes of ammonium assimilation (glutamine synthetase and glutamate synthase) were also found mainly in these cells (see Edwards and Huber, ref. 9), rather than in the Kranz cells. No conclusions were drawn about the significance of such a distribution. 

Enzyme Pathway enzyme/nitrite reductase (fraction of total) Chloroplast distribution (% total)... 

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