title: Purification and properties of nitrite reductase from Escherichia coli K12.
abstract: NADH-nitrite oxidoreductase (EC 1.6.4) was purified to better than 95% homogeneity from batch cultures of Escherichia coli strain OR75Ch15, which is partially constitutive for nitrite reductase synthesis. Yields of purified enzyme were low, mainly because of a large loss of activity during chromatography on DEAE-cellulose. The quantitative separation of cytochrome c-552 from nitrite reductase activity resulted in an increase in the specific activity of the enzyme: this cytochrome is not therefore an integral part of nitrite reductase. The subunit molecular weights of nitrite reductase and of a haemoprotein contaminant, as determined by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, were 88000 and 80000 respectively. The sedimentation coefficient was calculated to be in the range 8.5-9.5S, consistent with a mol.wt. of 190000. It is suggested therefore that the native enzyme is a dimer with two identical or similar-sized subunits. Purest samples contained 0.4 mol of flavin/mol of enzyme, but no detectable haem. Catalytic activity was totally inhibited by 20 micron-p-chloromercuribenzoate and 1 mM-cyanide, slightly inhibited by 1 micron-sulphite and 10mM-arsenite, but insensitive to 1 mM-2,2'-bipyridine, 4mM-1,10-phenanthroline and 10mM-NaN3. Three molecules of NADH were oxidized for each NO2-ion reduced: the product of the reaction is therefore assumed to be NH4+. The specific activity of hydroxylamine reductase increased at each step in the purification of nitrite reductase, and the elution profiles for these two activities during chromatography on DEAE-Sephadex were coincident. It is likely that a single enzyme is responsible for both activities.
mesh_terms: D002499:Centrifugation, Density Gradient; D003574:Cytochrome c Group / Q000302:isolation & purification; D004926:Escherichia coli / Q000201:enzymology* / Q000254:growth & development; D006420:Hemeproteins / Q000302:isolation & purification; D006898:Hydroxylamines; D008970:Molecular Weight; D009247:NADH, NADPH Oxidoreductases / Q000302:isolation & purification*; D009572:Nitrite Reductases / Q000037:antagonists & inhibitors / Q000302:isolation & purification*
chemical_list: D003574:Cytochrome c Group; D006420:Hemeproteins; D006898:Hydroxylamines; D009247:NADH, NADPH Oxidoreductases; D009572:Nitrite Reductases