TABLE 4.

Electron acceptor specificity of OOR

Electron acceptor	Activity
	μmol min−1mg−1
Methyl viologen (20 μm)	0.047 ± 0.008
Metronidazole (20 μm)	0.014 ± 0.002
Ferredoxin (20 μm)	0.029 ± 0.001
Cytochrome c (20 μm)	0.182 ± 0.004
NAD+ (20 μm or 1 mm)	NDa
NADP+ (20 μm or 1 mm)	ND
FAD (20 μm)	0.049 ± 0.008
FMN (20 μm)	0.057 ± 0.004
CODH (20 μm)	0.006 ± 0.001b

^a ND, not detected with 230 μg of enzyme in a 1-ml assay.

^b Measured at pH 7.0, where CO₂ reduction by CODH with dithionite as a reductant was 4.7 μmol min⁻¹ μmol CODH⁻¹. OOR activity is approximately 3-fold less at pH 7 than at pH 8 with methyl viologen as electron acceptor, and OOR is inhibited by CO₂, with approximately half as much activity under 6.8 mm CO₂ as with no CO₂.