TABLE 2.

Catalytic properties of the FNR_L-PC and FNR_S isoforms

FNR catalytic properties (unit)	FNRL-PC	FNRS
Ferricyanide reductase activity
Km(NADPH) (μm)	40 ± 3	55 ± 5
kcat(s−1)	124 ± 3	174 ± 5
kcat/Km (μm−1s−1)	3.1 ± 0.3	3.2 ± 0.4
Cytochrome c reductase activity
Km(Fd) (μm)	47 ± 6	28 ± 2
kcat (s−1)	144 ± 12	154 ± 6
kcat/Km (μm−1s−1)	3.1 ± 0.7	5.5 ± 0.6
Single reduction of FNR by Fdred
no NADP+
Second-order forward rate k1 (μm−1s−1)	14.1	24.9
Second-order reverse rate k−1(μm−1s−1)	4.6	10.6
Keq = k1/k−1	3.06	2.35
Em(FNRox/FNRsq)a (mV)	−384	−390
1 mm NADP+
Second-order forward rate k1 (μm−1s−1)	10.8	15.2
Second-order reverse rate k−1 (μm−1s−1)	4.0	5.4
Keq = k1/k−1	2.73	2.84
Em(FNRox/FNRsq)a (mV)	−386	−385
Multiple turnover: Initial rate of reoxidation of 3.75 μm Fdred (reoxidized Fdred per second and per FNR)
Observed rate	50	53/(330)b
Calculated rate (with limiting k1)	40.5	57/(1564)b

^a Vs NHE. Calculated assuming E_{m(Fdox/Fdred)} = −412 mV (44).

^b Numbers in italics were obtained at low ionic strength and recalculated from Ref. 5 by using an absorption coefficient of 9,000 m⁻¹cm⁻¹ for FNR_S at 461 nm instead of 10,800 m⁻¹cm⁻¹ (giving e.g. k₁ = 417 μm⁻¹s⁻¹).