Periplasmic nitrate reductases

Thomas, G., Potter, L., and Cole, J. A., 1999,The periplasmic nitrate reductase from Escherichia coli a heterodimeric molyhdoprotein with a douhle-arginine signal sequence and an unusual leader peptide cleavage site, FEMS Microbiol. Lett. 174 167nl71. 

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. ... 

NapB. NapB is a subunit of the heterodimeric periplasmic nitrate reductase (NapAB) and transfers electrons to the catalytic NapA molybdoprotein. Nap systems are found in a number of bacteria, iucluding enterobacteria, aerobic denitrifiers, and nonsulfur purple photo synthetic bacteria. Their physiological function is different in these groups of bacteria and includes redox balancing using nitrate as an electron sink to dispose of excess rednctant, aerobic denitrification, and nitrate scavenging in nitrate-limited environments. 

Figure 2 The dissimilatory denitrification pathway. NO3 is reduced to NO2 by a membrane-bound or periplasmic nitrate reductase(NaR). N02 is reduced to NO by either a cytochrome cdi or copper nitrite reductase (NiR). NO is reduced to N2O by nitric oxide reductase (NOR). N2O is reduced to N2 by nitrous oxide reductase (N2OR). Electron transport from uhiquinol (UQH2) at NaR and the cyt hcj complex is coupled to generation of a proton gradient...

Flanagan, D. A., Gregory, L. G., Carter, J. P., Karakas-Sen, A., Itichardson, D. J., and Spiro, S. (1999). Detection of genes for periplasmic nitrate reductase in nitrate respiring bacteria and in community DNA. FEMS Microbiol. Lett 177, 26 i—210. 

Figure 3 Sequence alignment of the N-termini of ArrA and molybdenum-containing proteins. The sequences belong to the arsenate reductase of Chrysiogenes arsenatis C.a ArrA) (14), the polysulfide reductase of WoUnella succinogenes (Wii. PsrA), and the periplasmic nitrate reductases of Escherichia coli (E.c. NapA) and Pseudomonas sp. G-179 P.s. sp. NapA). Boxed amino acids show identity to C. arsenatis ArrA.

D. desulfuricans also showed a membrane-associated or soluble nitrate reductase catalyzing the respiratory reduction of nitrate to nitrite [ 134-136]. A cytochrome c-dependent nitrate reductase was also isolated from Geobacter metallireducens [137], Obviously, nitrate uptake and nitrite extrusion into the bulk phase is dispensable for periplasmic nitrate reductases. In addition, a periplasmic location of nitrate reductases will prevent the interaction of potentially toxic compounds such as nitrite or NO with cytoplasmic proteins. 

Non-exchangeable Couplings to the High-g Mo(v) Species in Periplasmic Nitrate Reductases... 

Cerqueira NMFSA, Fernandes PA, Gonzalez PJ, Moura JJG, Ramos MJ (2013) The sulfur shift an activation mechanism for periplasmic nitrate reductase and formate dehydrogenase. Inorg Chem 52 10766-10772. doi 10.1021/ic3028034... 

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