{"id":729,"date":"2026-04-15T13:22:40","date_gmt":"2026-04-15T13:22:40","guid":{"rendered":"https:\/\/citations.tools.bio-logic.fr\/?p=729"},"modified":"2026-04-15T13:22:40","modified_gmt":"2026-04-15T13:22:40","slug":"trapping-and-spectroscopic-characterization-of-an-feiii-superoxo-intermediate-from-a-nonheme-mononuclear-iron-containing-enzyme","status":"publish","type":"post","link":"https:\/\/citations.tools.bio-logic.fr\/?p=729","title":{"rendered":"Trapping and spectroscopic characterization of an Fe<sup>III<\/sup>-superoxo intermediate from a nonheme mononuclear iron-containing enzyme"},"content":{"rendered":"<h4>DOI:<\/h4>\n<p><a href=\"https:\/\/doi.org\/10.1073\/pnas.1010015107\" target=\"_blank\" rel=\"noopener\">10.1073\/pnas.1010015107<\/a><\/p>\n<h4>Authors:<\/h4>\n<p>Michael M. Mbughuni, Mrinmoy Chakrabarti, Joshua A. Hayden, Emile L. Bominaar, Michael P. Hendrich, Eckard M\u00fcnck, John D. Lipscomb<\/p>\n<h4>Abstract:<\/h4>\n<p>Fe(III)-O(2)*(-) intermediates are well known in heme enzymes, but none have been characterized in the nonheme mononuclear Fe(II) enzyme family. Many steps in the O(2) activation and reaction cycle of Fe(II)-containing homoprotocatechuate 2,3-dioxygenase are made detectable by using the alternative substrate 4-nitrocatechol (4NC) and mutation of the active site His200 to Asn (H200N). Here, the first intermediate (Int-1) observed after adding O(2) to the H200N-4NC complex is trapped and characterized using EPR and M\u00f6ssbauer (MB) spectroscopies. Int-1 is a high-spin (S(1) = 5\/2) Fe(III) antiferromagnetically (AF) coupled to an S(2) = 1\/2 radical (J \u2248 6 cm(-1) in ). It exhibits parallel-mode EPR signals at g = 8.17 from the S = 2 multiplet, and g = 8.8 and 11.6 from the S = 3 multiplet. These signals are broadened significantly by hyperfine interactions (A((17)O) \u2248 180 MHz). Thus, Int-1 is an AF-coupled species. The experimental observations are supported by density functional theory calculations that show nearly complete transfer of spin density to the bound O(2). Int-1 decays to form a second intermediate (Int-2). MB spectra show that it is also an AF-coupled Fe(III)-radical complex. Int-2 exhibits an EPR signal at g = 8.05 arising from an S = 2 state. The signal is only slightly broadened by (&lt; 3% spin delocalization), suggesting that Int-2 is a peroxo-Fe(III)-4NC semiquinone radical species. Our results demonstrate facile electron transfer between Fe(II), O(2), and the organic ligand, thereby supporting the proposed wild-type enzyme mechanism.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>DOI: 10.1073\/pnas.1010015107 Authors: Michael M. Mbughuni, Mrinmoy Chakrabarti, Joshua A. Hayden, Emile L. Bominaar, Michael P. Hendrich, Eckard M\u00fcnck, John D. Lipscomb Abstract: Fe(III)-O(2)*(-) intermediates are well known in heme enzymes, but none have been characterized in the nonheme mononuclear Fe(II) enzyme family. Many steps in the O(2) activation and reaction cycle of Fe(II)-containing homoprotocatechuate [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[],"class_list":["post-729","post","type-post","status-publish","format-standard","hentry","category-freeze-quench"],"_links":{"self":[{"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=\/wp\/v2\/posts\/729","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=729"}],"version-history":[{"count":0,"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=\/wp\/v2\/posts\/729\/revisions"}],"wp:attachment":[{"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=729"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=729"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=729"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}