. 2014 Jan 29;114(8):4229–4317. doi: 10.1021/cr4004709

Table 2. Spectroscopic Properties of the Radical SAM [4Fe–4S] FeS Cluster.

enzyme	organism	λ_max (nm)^a	sample type	EPR (g-values)^b	[4Fe–4S] cluster Mössbauer parameters (mm/s)^c	ref
Radical SAM Enzymes Without Auxiliary Fe–S Clusters
LAM	Clostridium subterminale SB4	420^f^,^h	as-isolated^f^,^h	2.03, 2.00, 1.99		(8, 22, 90)
			oxidized^f^,^h	2.03, 2.01
			reduced^f^,^h	–^j
			reduced + SAM^f^,^h	2.00, 1.90, 1.85
RNR-AE^p	Escherichia coli	420^e	as-isolated^e	2.03, 2.00	[4Fe–4S]²⁺: ∂ = 0.43; ΔE_Q = 1.0 (82%)^e	(7a, 91)
			reduced^e	2.03, 1.93; 2.02, 1.92	[4Fe–4S]²⁺: ∂ = 0.46; ΔE_Q1 = 1.04 (30%)^e
			reduced^e	2.03, 1.93; 2.02, 1.92	[4Fe–4S]⁺: (∂₁ = 0.53; ΔE_Q1 = 0.92, ∂₂ = 0.59; ΔE_Q2 = 1.61) (50%)^e
			reduced + SAM^e	2.00, 1.91	[4Fe–4S]²⁺: ∂ = 0.47; ΔE_Q = 1.00 (49%)
			reduced + SAM^e	2.00, 1.91	[4Fe–4S]⁺: (∂₁ = 0.62; ΔE_Q1 = 1.70, ∂₂ = 0.53; ΔE_Q2 = 0.73) (40%)^e
	Lactococcus lactis		as-isolated^e	2.03, 2.01, 2.00		(92)
			reduced^e^,^o	2.02, 1.93; 2.04, 1.94^o
			reduced + SAM^e	2.00, 1.92, 1.86; 2.00, 1.92, 1.86^o
PFL-AE	Escherichia coli	420^f	reduced^f^,^o	2.02, 1.94, 1.88^o		(5, 16a, 17)
			reduced + SAM^f^,^o	2.01, 1.89, 1.88; 2.01, 1.88, 1.87^o
			as-isolated^f		[4Fe–4S]²⁺: (∂₁ = 0.45; ΔE_Q1 = 1.15, ∂₂ = 0.45; ΔE_Q2 = 1.10) (8%)^f	(66, 93)
			reduced^f^,^o		[4Fe–4S]²⁺: (∂₁ = 0.45; ΔE_Q1 = 1.15, ∂₂ = 0.45; ΔE_Q2 = 1.10) (66%)^f
			reduced^f^,^o		[4Fe–4S]⁺: (∂₁ = 0.50; ΔE_Q1 = 1.32, ∂₂ = 0.58; ΔE_Q2 = 1.89) (12%)^f
			as-isolated + SAM^f^,^q		[4Fe–4S]²⁺: (∂ = 0.72; ΔE_Q = 1.15) (32%)^f^,^q
			as-isolated + dAdoH^f		[4Fe–4S]²⁺: (∂ = 0.44; ΔE_Q = 1.20) (19%) (∂₁ = 0.39; ΔE_Q1 = 0.52), (∂₂ = 1.00; ΔE_Q2 = 2.07) (77%)
			whole cells		[4Fe–4S]²⁺: (∂₁ = 0.43; ΔE_Q1 = 1.20), (∂₂ = 0.45; ΔE_Q2 = 0.71), (∂₃ = 0.97; ΔE_Q3 = 2.08) (75%)
		420^e	as-isolated^e	2.01		(94)
			reduced^e	2.03, 1.93
			reduced + SAM^e^,^m	2.01, 1.92, 1.89
			reduced + SAH^e^,^m	2.04, 1.93, 1.90
SPL	Bacillus subtilis	400, 472^d	as-isolated^d			(95)
		420^e	as-isolated^e	2.03	[4Fe–4S]²⁺: ∂ = 0.44; ΔE_Q = 1.06 (40%)^e	(96)
			reduced^e	2.03, 1.93
			reduced + SAM^e	2.02, 1.93
		420^f	as-isolated^f	2.02		(97)
			reduced^f	2.03, 1.93, 1.89; 2.04, 1.94, 1.89
			reduced + SAM^f	2.03, 1.93, 1.92
	Clostridium acetobutylicum	420^e	as-isolated^e		[4Fe–4S]²⁺: ∂ = 0.43; ΔE_Q = 1.09 (42%)^e	(98)
			as-isolated^f		[4Fe–4S]²⁺: ∂ = 0.45; ΔE_Q = 1.22 (27%)^f
			reduced^e	2.04, 1.94
		413^f	as-isolated^f	1.99		(74b)
			reduced^f	2.03, 1.93, 1.92
			reduced + SAM^f	2.03, 1.92, 1.82
	Geobacillus stearothermophilus	420^e	reduced^e	2.04, 1.93, 1.89		(99)
			reduced + SAM^e	2.04, 1.93, 1.89
HemN	Escherichia coli	410^f	as-isolated^f		[4Fe–4S]²⁺: ∂₁ = 0.43, ΔE_Q1 = 1.17 (67%); ∂₂ = 0.57; ΔE_Q2 = 1.23 (22%)^f	(85, 100)
			as-isolated + SAM^f		[4Fe–4S]²⁺: ∂₁ = 0.43, ΔE_Q1 = 1.10 (67%); ∂₂ = 0.68; ΔE_Q2 = 1.04 (22%)^f
			reduced^f	2.06, 1.94, 1.89
			reduced + SAM^f	–^j
ThiGH	Escherichia coli	390,^g 410^g	as-isolated^g	2.01		(101)
			reduced^g	2.03, 1.92
			reduced + SAM^g	2.00, 1.87
DesII	Streptomyces venezuelae	420^e	as-isolated^d	2.01		(87, 102)
			reduced^e	2.01, 1.96, 1.87
Elp3	Methanocaldococcus jannaschi	420^e	as-isolated^e	2.00, 1.96		(103)
			reduced^e	2.03, 1.93
			reduced + SAM^e	2.02, 1.93
AviX12	Streptomyces viridochromogenes	450^d	oxidized^d	2.03, 2.02, 2.00		(104)
			reduced^d	–^j
ThiC	Arabidopsis thaliana	410^d^,^f^,^l	as-isolated^d^,^l			(105)
	Salmonella enterica	410^f	as-isolated^f			(106)
			reduced^f	1.92
	Caulobacter crescentus	415^g	as-isolated^f		[4Fe–4S]²⁺: ∂ = 0.46; ΔE_Q = 1.11 (53%)^f	(41)
			as-isolated^g	2.00	[4Fe–4S]²⁺: ∂ = 0.45; ΔE_Q = 1.12 (43%)^g
			reduced^g	2.02, 1.93
Bss-AE^p	Thauera aromatica T1	420,^e 390^g	as-isolated^e^,^f^,^g	2.02	[4Fe–4S]²⁺: ∂ = 0.43; ΔE_Q = 1.09 (92%)^f^,^z	(107)
			reduced^e^,^g	2.04, 1.94;^e 2.06, 1.94^g
Dph2	Pyrococcus horikoshii	400^f	as-isolated^f		[4Fe–4S]²⁺: ∂ = 0.43; ΔE_Q = 1.13 (73%)^f	(32, 108)
			reduced^f	2.03, 1.92, 1.86
HcgA	Methanococcus maripaludis S2	410^g	as-isolated^g			(109)
			reduced^g	2.04, 1.93
			reduced + SAM^g	2.03, 1.92
NirJ	Paracoccus pantotrophus		as-isolated^f	–^j		(110)
			reduced^f	2.02, 1.93
			reduced + SAM^f	2.00, 1.89
RlmN	Escherichia coli	410^g	as-isolated^f^,^g^,^aa	N.R.ⁱ	[4Fe–4S]²⁺: ∂ = 0.44; ΔE_Q = 1.14 (93%);^f (95%)^g	(111)
Cfr	Staphylococcus aureus	400,^g 410^g	as-isolated^f^,^g^,^aa	N.R.ⁱ	[4Fe–4S]²⁺: ∂ = 0.44; ΔE_Q = 1.10 (86%);^f (98%)^g	(111, 112)
			reduced^g	2.04, 1.93, 1.89
			reduced + SAM^g	–^j
			reduced + SAH^g	2.00, 1.93, 1.82
Viperin	Homo sapiens	415,^e^,^g 410^d	as-isolated^g	2.01		(113)
			reduced^g	2.02, 1.92, 1.91
			reduced + SAM^g	2.03, 1.95, 1.88
GD-AE	Clostridium butyricum		reduced^g	N.R.ⁱ		(31)
NocL	Nocardia sp. ATCC 202099	393^g	as-isolated^g	–^j		(71)
			reduced^g	2.02, 1.91
			reduced + SAM^g	2.01, 1.89, 1.80^m
			reduced + Trp^g	2.02, 1.89, 1.85
NosL	Streptomyces actuosus	400^g	as-isolated^g			(114)
			reduced^g	2.02, 1.91
PhnJ	Escherichia coli	403,^e 410^g	reduced^g	2.01, 1.92, 1.87		(115)
PhpK	Kitasatospora phosalacinea	420^g	as-isolated^g	2.00		(116)
			reduced^g	1.93
CofH	Nostoc punctiforme	405^f	as-isolated^f			(117)
CofG	Methanocaldococcus jannaschii	420^f	as-isolated^f			(117)
QueE	Bacillus subtilis	410^g	as-isolated^g^,^aa	2.00	[4Fe–4S]²⁺: ∂ = 0.44; ΔE_Q = 1.13 (80%)^g	(88)
			reduced^g	–^j
			reduced + SAM^g	2.00, 1.91, 1.86
TsrM	Streptomyces laurentii	420^e	as-isolated^e			(89)
YtkT	Streptomyces sp. TP-A0356	410^g	as-isolated^g			(118)
GenK	Micromonospora echinospora	420^e	as-isolated^e			(84)
BlsE	Streptomyces griseochromogenes	420^g	as-isolated^g	2.01		(81)
			reduced^g	2.02, 1.93
			reduced + SAM^g	2.00, 1.96, 1.87
MqnE	Thermus thermophilus	415^f	as-isolated^f			(119)
Radical SAM Enzymes Coordinating Auxiliary Fe–S Clusters
BioB	Escherichia coli	410^d^,^k	as-isolated^d^,^k			(120)
		420^e^,^k	as-isolated^e^,^k		[4Fe–4S]²⁺: (∂₁ = 0.44; ΔE_Q1 = 1.13 (72%), ∂₂ = 0.85; ΔE_Q2 = 0.51 (8%))^e^,^k^,^t	(121)
			reduced^e^,^k	2.04, 1.93^e^,^k^,^t	[4Fe–4S]⁺: ∂ = 0.85; ΔE_Q = 0.51 (80%)^e^,^k^,^t
			as-isolated^e^,^k		[4Fe–4S]²⁺: ∂₁ = 0.45; ΔE_Q1 = 1.16^e^,^k^,^x	(122)
			as-isolated + SAM^e^,^k		[4Fe–4S]²⁺: (∂₁ = 0.45; ΔE_Q1 = 1.16; ∂₂ = 0.40; ΔE_Q2 = 0.86; ∂₃ = 0.64; ΔE_Q3 = 1.26)^e^,^k^,^x
			reduced^e^,^k^,^u	∼2.00, 1.94, 1.94
			reduced + SAM^e^,^k^,^u	∼2.00, 1.93, 1.85
LipA	Escherichia coli	420^e^,^k	as-isolated^e^,^k	–^j	∂ = 0.44; ΔE_Q = 1.20 (50%)^e^,^k	(121b, 123)
		420^e^,^k	reduced^e^,^k	2.04, 1.93
		413^f^,^k	reduced^f^,^k	2.06, 1.95, 1.92		(124)
		400^f^,^g^,^k^,ⁿ	as-isolated^f^,^g^,^k		[4Fe–4S]²⁺: (∂₁ = 0.45, ΔE_Q1 = 0.98; ∂₂ = 0.46, ΔE_Q2 = 1.30) (95%),^f^,^k (64%)^g^,^k	(125)
			as-isolated^f^,^g^,ⁿ		[4Fe–4S]²⁺: (∂₁ = 0.46, ΔE_Q1 = 0.92; ∂₂ = 0.45, ΔE_Q2 = 1.22) (95%),^f^,ⁿ (64%)^g^,ⁿ
			reduced^f^,^g^,^k	2.03, 1.93
			reduced^f,ⁿ	2.03, 1.93
MiaB	Escherichia coli	(416, 460, 560)^d^,^e^,^k	as-isolated^d^,^e^,^k	2.01		(126)
			reduced^d^,^e^,^k	2.06, 1.93
	Thermotoga maritima	420^e^,^k	as-isolated^e^,^k	2.01	[4Fe–4S]²⁺: (∂₁ = 0.46, ΔE_Q1= 1.27; ∂₂ = 0.44, ΔE_Q2 = 1.03) (71%) [4Fe–4S]⁺: (∂₁ = 0.50, ΔE_Q1 = 1.32; ∂₂ = 0.58, ΔE_Q2 = 1.89) (29%)^e^,^k	(24b, 127)
			reduced^e^,^k	2.05, 1.93
MoaA	Homo sapiens	415^d^,^k	as-isolated^g^,^k	2.00	[4Fe–4S]²⁺: ∂ = 0.48, ΔE = 1.26; (40%)^g^,^k^,ⁿ	(128)
MoaA	Homo sapiens	410^f^,^g^,^k	as-isolated^g^,^k	2.00	[4Fe–4S]²⁺: ∂ = 0.48, ΔE = 1.26; (40%)^g^,^k^,ⁿ	(128)
			reduced^g^,^k	2.03, 1.92, 1.89
HydE	Thermotoga maritima	400^e^,^k	as-isolated^e^,^k			(129)
			reduced^e^,^k	2.04, 1.93
HydG	Thermotoga maritima	400^e^,^k	reduced^e^,^k	N.R.ⁱ		(129)
	Clostridium acetobutylicum	400,^e^,^k 395^g^,^k	as-isolated^g^,^k			(78b, 130)
			reduced^g^,ⁿ^,^o	2.03, 1.91, 1.89
			reduced + SAM^g^,ⁿ^,^o	2.03, 1.92, 1.91; 1.99, 1.88, 1.84
	Shewanella oneidensis	N.R.ⁱ	reduced^g^,^m^,ⁿ	2.05, 1.94, 1.91		(131)
			reduced + SAM^g^,ⁿ	2.01, 1.88, 1.84
NifB	Azotobacter vinelandii	400^g^,^k	as-isolated^g^,^k			(132)
NifEN-B	Azotobacter vinelandii	N.R.^f^,ⁱ^,^k	oxidized^f^,^k			(133)
			reduced^f^,^k	2.02, 1.95, 1.94
			reduced + SAM^f	1.94^j^,^v
Hpd-AE^p	Clostridium scatologenes	420^g	as-isolated^g^,^r	2.02	[4Fe–4S]²⁺: ∂ = 0.44; ΔE_Q = 1.22 (82%)^g^,^z	(75, 134)
			reduced^g^,^r	2.04, 1.94
			reduced + SAM^g^,^r	2.04, 1.94
		390^f	as-isolated^f^,^s	–^j
			reduced^f^,^s	2.04, 1.94
			reduced + SAM^f^,^s	2.04, 1.94
	Clostridium difficile	385^f	as-isolated^s	–^j
			reduced^s	2.04, 1.94
			reduced + SAM^s	2.04, 1.94
anSME	Clostridium perifringens	420,^e^,^k 400^g^,^k	as-isolated^e^,^f^,^g^,^k		[4Fe–4S]²⁺: ∂ = 0.44; ΔE_qQ = 1.14 (95%);^f^,^k (75%)^g^,^k	(80b, 135)
			reduced^e^,^k	2.05, 1.94
			reduced + SAM^e^,^k	1.99, 1.90
	Bacteroides thetaiotaomicron	400^e^,^k	reduced^e^,^k	2.05, 1.92		(135b, 136)
			reduced + SAM^e^,^k	1.98, 1.90, 1.84
BtrN	Bacillus circulans	420^f^,^g^,^k	as-isolated^f^,^g^,^k		[4Fe–4S]²⁺: ∂ = 0.44; ΔE_qQ = 1.13 (87%),^f^,^k (98%)^g^,^k	(76, 137)
			reduced^g^,^k	2.04, 1.92
			reduced + SAM^g^,^k	1.99, 1.83
			reduced + SAM + substrate^g^,^k^,^w	2.05, 1.96, 1.87
AtsB	Klebsiella pneumoniae	395^f^,^g^,^k^,^aa	as-isolated^g	N.R.ⁱ	[4Fe–4S]²⁺: ∂ = 0.44; ΔE_Q = 1.17 (94%)^f^,^g	(79, 80b)
RimO	Escherichia coli	410^f^,^g^,^k	as-isolated^f^,^k	2.01	[4Fe–4S]²⁺: ∂ = 0.43, ΔE_Q = 1.07 (90%)^f^,^k	(138)
			as-isolated + SAM^f^,^k		[4Fe–4S]²⁺: (∂₁ = 0.43, ΔE_Q1 = 1.07 (58%); ∂₂ = 0.70, ΔE_Q2 = 1.24 (16%); ∂₃ = 0.37, ΔE_Q3 = 0.81 (16%))^f^,^k
			as-isolated^g^,^k		[4Fe–4S]²⁺: ∂ = 0.43, ΔE_Q = 1.12 (62%)^g^,^k
			as-isolated + SAM^g^,^k		[4Fe–4S]²⁺: (∂₁ = 0.43, ΔE_Q1 = 1.12 (44%); ∂₂ = 0.70, ΔE_Q2 = 1.24 (9%); ∂₃ = 0.37, ΔE_Q3 = 0.81 (9%))^g^,^k
			reduced^f^,^k	2.06, 1.98, 1.94
			reduced^g^,^k	2.04, 1.93
			reduced + SAM^g^,^k	2.04, 1.93
	Thermotoga maritima	420^e^,^f^,^g^,^k	as-isolated^e^,^f^,^g^,^k		[4Fe–4S]²⁺: ∂₁ = 0.45, ΔE_Q1 = 1.15 (56%); (∂₂ = 0.48, ΔE_Q2 = 1.24; ∂₃ = 0.60, ΔE_Q3 = 2.07; ∂₄ = 0.30, ΔE_Q4 = 0.90) (32%)^e^,^k	(83, 139)
			reduced^e^,^k	2.03, 1.93, 1.90; 2.04, 1.94, 1.88
			reduced^e^,^k^,^aa	2.03, 1.93, 1.90; 2.05, 1.94, 1.88	[4Fe–4S]⁺: (∂₁ = 0.55, ΔE_Q1 = 1.90; ∂₂ = 0.50, ΔE_Q2 = 1.30)^e^,^k
PqqE	Klebsiella pneumoniae	420^e^,^k	as-isolated^e^,^k	2.05, 1.94		(140)
		420^g^,^k	as-isolated^g^,^k	2.01
			reduced^g^,^k	2.06, 1.96, 1.91
			reduced + SAM^g^,^k	2.00, 1.94, 1.90^m
YqeV^y	Bacillus subtilis	420^e^,^k	reduced^e^,^k	N.R.ⁱ		(141)
TYW1	Pyrococcus abyssi	410^e^,^k	as-isolated^e^,^k			(142)
			as-isolated + SAM^e^,^k		[4Fe–4S]²⁺: ∂ = 0.44; ΔE_Q = 1.13 (78%)^e^,^k
			reduced^e^,^k^,^o	2.02, 1.90, 1.86
			reduced + SAM^e^,^k^,^o	1.98, 1.86, 1.83
AlbA	Bacillus subtilis	410^e^,^k	as-isolated^e^,^k	–^j		(86)
			reduced^e^,^k	2.03, 1.92
		430^e^,ⁿ	as-isolated^e^,ⁿ	2.01
			reduced^e^,ⁿ	2.03, 1.92
FbiC	Thermobifida fusca	420^e	as-isolated^e			(117)
SkfB	Bacillus subtilis	410^e^,^k	as-isolated^e^,^k	2.01		(143)
			reduced^e^,^k	2.04, 1.93
		410^e^,ⁿ	as-isolated^e^,ⁿ	2.01
			reduced^e^,ⁿ	2.03, 1.93

Represents nonreduced λ_max with as-reconstituted enzyme. Exceptions are marked as indicated.

Represents spectral g-values for the radical SAM [4Fe–4S] cluster; however, overlapping [4Fe–4S] cluster signals may be reflected in the cited g-values. Spectral values where radical SAM [4Fe–4S] signal discrimination has been performed is indicated. Unless otherwise indicated, samples that underwent reduction were reduced with dithionite.

Represents selected (simulated) Mössbauer parameters consistent with the radical SAM [4Fe–4S] cluster. Unless otherwise indicated, spectral values reported at 4.2 K.

Aerobic purification, no Fe–S reconstitution.

Aerobic purification, anaerobic Fe–S reconstitution.

Anaerobic purification, no Fe–S reconstitution

Anaerobic purification and Fe−S reconstitution.

Enzyme not Fe–S reconstituted, but undergoes activation with Fe.

ⁱ

N.R. = data available, but was not reported.

Diamagnetic.

Intact enzyme.

Truncated enzyme.

Additional spectral features observed; please see reference.

ⁿ

Site-directed mutagenesis performed on non-radical SAM Fe–S cluster.

5-Deazariboflavin reduction data available.

Radical SAM Fe–S cluster part of a larger oligomeric structure with subunits that coordinate Fe–S clusters.

Represents a mixed ⁵⁶Fe/⁵⁷Fe [4Fe–4S] cluster.

Enzyme purified with a hexahistidine tag.

Enzyme purified with a streptavidin tag.

Spectrum from Ollagnier 2000 Biochemistry.^121b Cited references have slightly different but comparable Mössbauer parameters.

Samples underwent cryoreduction.

SAM serves as a substrate, causing Fe–S cluster to become diamagnetic.

Assignment was made before discovery of an auxiliary cluster on the enzyme.

% Fe not reported.

Reference uses YqeV and MtaB interchangeably.

Experiment performed at 80 K.

^aa

EPR or UV–vis spectral data available on ⁵⁷Fe-enriched (reconstituted) samples.