Haem-staining analysis E. meliloti cells grown aerobically in 150 ml of TY medium were harvested selleck by centrifugation at 8000 g for 5 min, washed twice with MM, resuspended in 200 ml of MM or

MMN at an OD600 of 0.15-0.2 and incubated under 2% initial O2 or anoxic (filled bottles) conditions for 24 h. The cell pellets were resuspended in 3 ml of 50 mM potassium phosphate buffer (pH 7) containing 100 μM 4-(2-aminoethyl) benzene-sulfonyl fluoride hydrochloride (ABSF), RNAse (20 μg · ml-1) and DNAse I (20 μg · ml-1). The cells were disrupted using a French pressure cell at a constant pressure of approximately 1000 psi (SLM Aminco, Jessup, MD, USA). The cell extract was centrifuged at 10,000 g for 20 min to remove the unbroken cells, and the supernatant was centrifuged at 140,000 g for 1 h. The membrane pellet was resuspended in 100 μl of the same buffer. The membrane

protein aliquots were diluted in sample buffer [124 mM Tris–HCl, pH 7.0, 20% glycerol, 4.6% sodium dodecyl sulphate (SDS) and 50 mM 2-mercaptoethanol] and incubated at room temperature for 10 min. The membrane proteins were separated at 4°C using 12% SDS-polyacrylamide gel electrophoresis, 4SC-202 chemical structure transferred to a nitrocellulose membrane and stained for haem-dependent peroxidase activity, as described previously [45], using the SuperSignal chemiluminescence detection kit (Pierce, Thermo Fisher Scientific, IL, USA). Analytical methods The nitrite JQ-EZ-05 mouse concentration was estimated after diazotisation by adding the sulphanilamide/naphthylethylene diamine dihydrochloride reagent [46]. The protein concentration was estimated using the Bradford method (Bio-Rad Laboratories, Richmond, CA) with a standard curve constructed with varying bovine serum albumin concentrations. Nitric oxide determination E. meliloti cells were incubated at an OD600 of 0.15-0.2 in MMN under 2% initial O2 or anoxic conditions, harvested and washed similar to the NR or Nir activity assays. Nitric oxide was measured amperometrically with a 2-mm ISONOP electrode APOLO 4000® (World Precision Inst., Sarasota, FL, USA) in

a 3-ml thermostatted and magnetically stirred reaction chamber [47]. The membrane-covered electrode was situated at the Acyl CoA dehydrogenase bottom of the chamber above the stirrer, and the reactants were injected using a Hamilton syringe through a port in the glass stopper. To determine the net production of NO, the 3-ml cuvette was filled with 1.410 ml of 25 mM phosphate buffer (pH 7.4), 250 μl (0.1-0.2 mg protein) of a cellular solution, 100 μl of an enzymatic mix containing glucose oxidase (Aspergillus niger) (80 units/2 ml) and catalase (bovine liver) (500 units/2 ml), 90 μl of 1 M sodium succinate and 100 μl of 320 mM glucose. When oxygen was consumed and a steady base line was observed, 50 μl of 1 M NaNO2 was added to the cuvette to begin the reaction. Each assay was continued until NO was detected.