Synonyms: a 4Fe-4S iron-sulfur cluster, a 4Fe-4S center, a 4Fe-4S cluster, a 4Fe-4S iron-sulfur center, a Fe4S4 iron-sulfur center, a [4Fe-4S] iron-sulfur center, [4Fe-4S], 4Fe-4S
|Superclasses:||a cofactor → a prosthetic group → a metal-sulfur cluster → an iron-sulfur cluster|
Iron-sulfur centers consist of nonheme iron complexed to sulfur in several ways. Iron-sulfur clusters are prosthetic groups of many proteins, which function as intracellular electron carriers with a low reduction potential. In addition to their roles in electron transfer reactions, iron-sulfur clusters are also known to participate in the activation of substrates, the stabilization of radicals and structures, the protection of proteins from enzymes and the storage of iron and sulfur. In addition, they act as sensors of iron, dioxygen, the superoxide ion, and possibly nitric oxide, and participate in gene expression [Park06a].
[4Fe-4S] iron-sulfur clusters feature four iron ions and four sulfide ions placed at the vertices of a cubane-type structure. The Fe centers are typically further coordinated by cysteinyl ligands.
Two main types of [4Fe-4S] iron-sulfur clusters are low-potential (bacterial-type) clusters and high-potential (HiPIP) clusters. The bacterial clusters shift between the oxidation states +1 and +2, while the HiPIP clusters shift between the oxidation states +2 and +3.
In some enzymes the [4Fe-4S] iron-sulfur clusters bind substrates and are thus classified as enzyme cofactors. For example, in radical SAM enzymes the cluster binds and reduces S-adenosylmethionine, generate a radical that interacts with the enzyme's substrate.
Chemical Formula: S4Fe4
Molecular Weight: 351.63 Daltons
Monoisotopic Molecular Weight: 351.62805116 Daltons
Standard Gibbs Free Energy of Formation (ΔfG'° in kcal/mol): 0.0
This compound has been characterized as a cofactor or prosthetic group of the following enzymes: 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate synthase, formate dehydrogenase N, ubiquinol:nitrate oxidoreductase (periplasmic), hydrogen:menaquinone oxidoreductase, pyruvate formate-lyase activating enzyme, lipoyl synthase, dimethyl sulfoxide reductase, tRNA m2A37 methyltransferase, carbon-phosphorous lyase, sulfite reductase, succinate:quinone oxidoreductase, ribonucleoside triphosphate reductase activase, quinolinate synthase, menaquinol:nitrate oxidoreductase, NADH:ubiquinone oxidoreductase (H+-transporting), coproporphyrinogen III dehydrogenase, fumarate reductase, fumarase A, protein methylthiotransferase, 23S rRNA m2A2503 methyltransferase, lysine 2,3-aminomutase, (2R,3S)-2-methylisocitrate hydro-lyase, 23S rRNA m5U1939 methyltransferase, 2,3-dihydroxy-3-methylvalerate hydro-lyase, 2,3-dihydroxy-isovalerate dehydratase, biotin synthase, D-threo-isocitrate hydro-lyase, D-threo-isocitrate hydro-lyase (cis-aconitate-forming), citrate hydro-lyase, citrate hydro-lyase (cis-aconitate-forming), serine deaminase, L-serine deaminase, L-serine deaminase, pyruvate formate-lyase activating enzyme, 2,4-dienoyl-CoA reductase
Park06a: Park YJ, Yoo CB, Choi SY, Lee HB (2006). "Purifications and characterizations of a ferredoxin and its related 2-oxoacid:ferredoxin oxidoreductase from the hyperthermophilic archaeon, Sulfolobus solfataricus P1." J Biochem Mol Biol 39(1);46-54. PMID: 16466637
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