10.1021\/bi0526276<\/a><\/p>\nAuthors:<\/h4>\n
Gang Xing, Eric W. Barr, Yinghui Diao, Lee M. Hoffart, K. Sandeep Prabhu, Ryan J. Arner, C. Channa Reddy, Carsten Krebs, J. Martin Bollinger<\/p>\n
Abstract:<\/h4>\n
myo-Inositol oxygenase (MIOX) catalyzes the ring-cleaving, four-electron oxidation of its cyclohexan-(1,2,3,4,5,6-hexa)-ol substrate (myo-inositol, MI) to d-glucuronate (DG). The preceding paper [Xing, G., Hoffart, L. M., Diao, Y., Prabhu, K. S., Arner, R. J., Reddy, C. C., Krebs, C., and Bollinger, J. M., Jr. (2006) Biochemistry 45, 5393-5401] demonstrates by M\u00f6ssbauer and electron paramagnetic resonance (EPR) spectroscopies that MIOX can contain a non-heme dinuclear iron cluster, which, in its mixed-valent (II\/III) and fully oxidized (III\/III) states, is perturbed by binding of MI in a manner consistent with direct coordination. In the study presented here, the redox form of the enzyme that activates O(2) has been identified. l-Cysteine, which was previously reported to accelerate turnover, reduces the fully oxidized enzyme to the mixed-valent form, and O(2), the cosubstrate, oxidizes the fully reduced form to the mixed-valent form with a stoichiometry of one per O(2). Both observations implicate the mixed-valent, diiron(II\/III) form of the enzyme as the active state. Stopped-flow absorption and freeze-quench EPR data from the reaction of the substrate complex of mixed-valent MIOX [MIOX(II\/III).MI] with limiting O(2) in the presence of excess, saturating MI reveal the following cycle: (1) MIOX(II\/III).MI reacts rapidly with O(2) to generate an intermediate (H) with a rhombic, g < 2 EPR spectrum; (2) a form of the enzyme with the same absorption features as MIOX(II\/III) develops as H decays, suggesting that turnover has occurred; and (3) the starting MIOX(II\/III).MI complex is then quantitatively regenerated. This cycle is fast enough to account for the catalytic rate. The DG\/O(2) stoichiometry in the reaction, 0.8 +\/- 0.1, is similar to the theoretical value of 1, whereas significantly less product is formed in the corresponding reaction of the fully reduced enzyme with limiting O(2). The DG\/O(2) yield in the latter reaction decreases as the enzyme concentration is increased, consistent with the hypothesis that initial conversion of the reduced enzyme to the MIOX(II\/III).MI complex and subsequent turnover by the mixed-valent form is responsible for the product in this case. The use of the mixed-valent, diiron(II\/III) cluster by MIOX represents a significant departure from the mechanisms of other known diiron oxygenases, which all involve activation of O(2) from the II\/II manifold.<\/p>\n","protected":false},"excerpt":{"rendered":"
DOI: 10.1021\/bi0526276 Authors: Gang Xing, Eric W. Barr, Yinghui Diao, Lee M. Hoffart, K. Sandeep Prabhu, Ryan J. Arner, C. Channa Reddy, Carsten Krebs, J. Martin Bollinger Abstract: myo-Inositol oxygenase (MIOX) catalyzes the ring-cleaving, four-electron oxidation of its cyclohexan-(1,2,3,4,5,6-hexa)-ol substrate (myo-inositol, MI) to d-glucuronate (DG). The preceding paper [Xing, G., Hoffart, L. M., Diao, Y., […]<\/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":[41],"class_list":["post-676","post","type-post","status-publish","format-standard","hentry","category-freeze-quench","tag-biochemistry"],"_links":{"self":[{"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=\/wp\/v2\/posts\/676","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=676"}],"version-history":[{"count":0,"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=\/wp\/v2\/posts\/676\/revisions"}],"wp:attachment":[{"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=676"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=676"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=676"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}