. Author manuscript; available in PMC: 2017 Jul 8.

Published in final edited form as: Biochemistry. 2016 Jun 14;55(25):3514–3527. doi: 10.1021/acs.biochem.6b00528

Table 1.

EPR Spectroscopic Properties of the [2Fe-2S]⁺, [3Fe-4S]⁺, and [4Fe-4S]⁺ Clusters Associated with HydF, PFL-AE, and HydE

enzyme	cluster type	T_OPT^b (K)	P_1/2^c (≤15 K) (mW)	b^d (≤15 K)	P_1/2 (30 K) (mW)	b^d (30 K)
PFL-AE
as-isolated	[3Fe-4S]⁺	<20	12.4	1.0	N/A^c	N/A
as-isolated	[2Fe-2S]⁺	~30	N/A	N/A	8.90	1.4
HydE^a
DT reduced	[4Fe-4S]⁺	<15	39.9	1.0	N/A	N/A
as-isolated	[3Fe-4S]⁺	<20	≥50.0	N/A	N/A	N/A
as-isolated	[2Fe-2S]⁺	~30	0.720	1.1	13.0	1.0
HydF
freshly purified	[2Fe-2S]⁺	25–30	0.270	1.0	11.5	1.1
freshly purified, photoreduced^f	[4Fe-4S]⁺	<15	≥50.0	N/A	N/A	N/A
freshly purified, photoreduced^f	[2Fe-2S]⁺	25–30	0.100	1.3	12.5	1.4
HydF
as-isolated	[3Fe-4S]⁺	<20	14.0	1.0	N/A	N/A
as-isolated	[2Fe-2S]⁺	25–30	0.190	1.4	10.4	1.2
as-isolated, photoreduced^f	[4Fe-4S]⁺	<15	≥50.0	N/A	N/A	N/A

The [4Fe-4S]⁺ cluster signal properties reported here are for the reduced enzyme in the presence of exogenous SAM.

T_OPT is defined as the temperature at which maximal peak to peak signal intensity is observed at 1 mW power.

Temperature values for reported P_1/2 measurements range between 12–15 K.

The term “b” represents the inhomogeneity parameter, as described in ref 43.

N/A, not applicable.

Measurements made on samples following an anaerobic thaw and freeze event.