TABLE 2.

Kinetic parameters of electron transfer by FprA and FprB, determined using the ferric reductase assay^a

Electron acceptor and electron donor	Flavin	Avg ± SD
		kcat (s−1)	Km (μM)	kcat/Km (s−1 μM−1)
Fe(III)-citrate
NADPH
FprA	Nonflavin	7.13 ± 0.11	4.59 ± 0.11	1.57 ± 0.16
	FAD	7.54 ± 0.31	6.36 ± 0.43	1.19 ± 0.13
	FMN	37.61 ± 1.32	6.25 ± 0.71	6.04 ± 0.48
FprB	Nonflavin	11.92 ± 0.30	5.87 ± 0.23	2.09 ± 0.28
	FAD	10.77 ± 0.63	11.77 ± 0.22	0.93 ± 0.02
	FMN	21.72 ± 0.47	13.19 ± 0.49	1.70 ± 0.03
NADH
FprA	Nonflavin	3.11 ± 0.06	107.64 ± 4.91	0.03 ± 0.004
	FAD	10.01 ± 0.44	12.38 ± 0.92	0.93 ± 0.03
	FMN	7.71 ± 0.12	2.73 ± 0.03	2.87 ± 0.08
FprB	Nonflavin	10.64 ± 0.72	3.38 ± 0.14	3.27 ± 0.04
	FAD	19.24 ± 0.24	6.16 ± 0.08	3.13 ± 0.03
	FMN	16.44 ± 0.15	2.35 ± 0.04	7.09 ± 0.10
Fe(III)-EDTA
NADPH
FprA	Nonflavin	6.18 ± 0.05	4.57 ± 0.11	1.32 ± 0.08
	FAD	6.80 ± 0.52	7.51 ± 0.27	0.84 ± 0.04
	FMN	11.18 ± 0.18	6.66 ± 0.09	1.68 ± 0.05
FprB	Nonflavin	1.91 ± 0.02	29.67 ± 0.57	0.09 ± 0.001
	FAD	10.28 ± 0.09	14.24 ± 0.11	0.72 ± 0.01
	FMN	20.38 ± 0.49	15.44 ± 0.91	0.77 ± 0.02
NADH
FprA	Nonflavin	5.60 ± 0.06	56.25 ± 0.62	0.11 ± 0.01
	FAD	10.18 ± 0.01	18.66 ± 0.26	0.55 ± 0.04
	FMN	9.18 ± 0.11	8.66 ± 0.26	1.06 ± 0.09
FprB	Nonflavin	8.21 ± 0.09	7.01 ± 0.08	1.17 ± 0.04
	FAD	13.20 ± 0.38	12.90 ± 0.57	1.06 ± 0.02
	FMN	17.47 ± 0.13	6.50 ± 0.03	2.69 ± 0.03

^aEach experiment was repeated three times.