Nitrite reductase occurrence

In order to check whether the occurrence of the Rieske-type sequence motif is unique for the assimilatory nitrite reductase from Bacillus subtilis, the sequences of other assimilatory nitrite reductases were searched for the presence of the four putative ligands of Rieske-type clusters. A well-conserved sequence pattern... 

Occurrence S. is the prosthetic group of sulfite and nitrite reductases of numerous bacteria and plants. S. plays an important part in the global nitrogen and sulfur cycles. The reduced, metal-free chromophore [si-rohydrochlorin, C42H46N40,6, Mr 862.84, uv, , (oc-... 

In the biochemical context, it has been well noted that the chemistry of NO (and of its conjugated acid, FINO (i8)) is quite distinct from that of NO (22). Its occurrence in catalytic cycles of NO synthase, nitrite reductase, and nitric oxide reductase (NOR) has been postulated (23). For example, in the multi-iron containing enzyme NOR two NO molecules are converted reductively to nitrous oxide, N2O, with nitroxyl (NO ), and hyponitrite (N202 ) (24) as putative intermediates (23). 

Yamashina and co-workers (94, 95) showed that azoxy-, azo- and hydrazo-com-pounds were not reduced by bacterial nitroreductase. Their results supported the observations of Saz and coworkers (78, 78, 80, 81) on the occurrence of individual nitro andnitroso reductase activities, and inhibitor studies indicated the involvement of metals in enzymatic activity. Furthermore, these studies contradicted the earlier work of Egami et al. (24) which indicated that nitroreductase activity could be attributed to nitrite reductase. 

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