An electrogenic nitric oxide reductase

Abstract

Nitric oxide reductases (Nors) are members of the heme‐copper oxidase superfamily that reduce nitric oxide (NO) to nitrous oxide (N2O). In contrast to the proton‐pumping cytochrome oxidases, Nors studied so far have neither been implicated in proton pumping nor have they been experimentally established as electrogenic. The copper‐A‐dependent Nor from Bacillus azotoformans uses cytochrome c 551 as electron donor but lacks menaquinol activity, in contrast to our earlier report (Suharti et al., 2001). Employing reduced phenazine ethosulfate (PESH) as electron donor, the main NO reduction pathway catalyzed by CuANor reconstituted in liposomes involves transmembrane cycling of the PES radical. We show that CuANor reconstituted in liposomes generates a proton electrochemical gradient across the membrane similar in magnitude to cytochrome aa 3, highlighting that bacilli using CuANor can exploit NO reduction for increased cellular ATP production compared to organisms using cNor.

Homeostatic control of nitric oxide (NO) at nanomolar concentrations in denitrifying bacteria – modelling and experimental determination of NO reductase kinetics in vivo in Paracoccus denitrificans

“…mol N 2 O mol −1 c Nor s −1 ). Such high k cat values are very unusual (Bar‐Even et al ., ); the values are 48–73 times higher than the k cat (≈40 s −1 ) estimated for P. denitrificans c Nor, produced in Escherichia coli (Thorndycroft et al ., ) and 24–35 times higher than the k cat (≈82 s −1 ) determined by Al‐Attar and de Vries ().…”

“…A v max NO = 3.56 fmol NO cell −1 h −1 is equivalent to 0.6 × 10 6 NO‐molecules cell −1 s −1 or 0.3 × 10 6 N 2 O molecules cell −1 s −1 . If we assume that each cell contains 3200–4800 c Nor molecules (see http://onlinelibrary.wiley.com/doi/10.1111/1462-2920.13129/suppinfo), we arrive at k cat values ranging from 62 to 94 N 2 O s −1 , which are higher than that determined for c Nor expressed in E. coli ≈ 40 N 2 O s −1 (Thorndycroft et al ., ), but encompass the recently measured turnover rates for purified c Nor reconstituted in liposomes ≈ 82 N 2 O s −1 (Al‐Attar and de Vries, ). Given that K 1NO ≪ K 2NO under steady‐state conditions, the reduced c Nor contains a “permanently” bound molecule of NO.…”

Nitrous Oxide Metabolism in Nitrate-Reducing Bacteria

“…An unusual qNor subgroup (qCu A Nor), exemplified by the enzyme from B. azotoformans, contains NorB in a complex with a subunit harbouring a Cu A site (typically found in oxygen-reducing HCOs), which makes this enzyme competent in receiving electrons from membrane-bound cytochrome c 551 in addition to the menaquinol pool (de Vries et al, 2007). However, it has been recently reported that the Bacillus enzyme lacks menaquinol activity and has changed its name from qCu A Nor to Cu A Nor (Al-Attar & de Vries, 2015).…”

Analysis of multiple haloarchaeal genomes suggests that the quinone‐dependent respiratory nitric oxide reductase is an important source of nitrous oxide in hypersaline environments

“…The single subunit has a catalytic C‐terminal domain that is substantially homologous to NorB, which is fused to a N‐terminal extension that is proposed to mediate electron transfer from quinol (Cramm et al ., ). Cu A Nor This is a distinctive two‐subunit enzyme recently described in Bacillus azotoformans that is characterised by a catalytic subunit whose structure is closer to that of cytochrome ba 3 terminal oxidase than to NorB. Instead of a c ‐type heme subunit II contains a dinuclear Cu A site which receives electrons from the physiological donor, cytochrome c 551 (Suharti et al ., ; Al‐Attar and de Vries, ).…”