10.1074\/jbc.ra117.000830<\/a><\/p>\nAuthors:<\/h4>\n
Bennett R. Streit, Arianna I. Celis, Garrett C. Moraski, Krista A. Shisler, Eric M. Shepard, Kenton R. Rodgers, Gudrun S. Lukat-Rodgers, Jennifer L. DuBois<\/p>\n
Abstract:<\/h4>\n
The H2<\/sub>O2<\/sub>-dependent oxidative decarboxylation of coproheme III is the final step in the biosynthesis of heme b<\/i> in many microbes. However, the coproheme decarboxylase reaction mechanism is unclear. The structure of the decarboxylase in complex with coproheme III suggested that the substrate iron, reactive propionates, and an active-site tyrosine convey a net 2e–<\/sup>\/2H+<\/sup> from each propionate to an activated form of H2<\/sub>O2<\/sub> Time-resolved EPR spectroscopy revealed that Tyr-145 formed a radical species within 30 s of the reaction of the enzyme-coproheme complex with H2<\/sub>O2<\/sub> This radical disappeared over the next 270 s, consistent with a catalytic intermediate. Use of the harderoheme III intermediate as substrate or substitutions of redox-active side chains (W198F, W157F, or Y113S) did not strongly affect the appearance or intensity of the radical spectrum measured 30 s after initiating the reaction with H2<\/sub>O2<\/sub>, nor did it change the \u223c270 s required for the radical signal to recede to \u226410% of its initial intensity. These results suggested Tyr-145 as the site of a catalytic radical involved in decarboxylating both propionates. Tyr-145\u2022<\/sup> was accompanied by partial loss of the initially present Fe(III) EPR signal intensity, consistent with the possible formation of Fe(IV)=O. Site-specifically deuterated coproheme gave rise to a kinetic isotope effect of \u223c2 on the decarboxylation rate constant, indicating that cleavage of the propionate C\u03b2-H bond was partly rate-limiting. The inferred mechanism requires two consecutive hydrogen atom transfers, first from Tyr-145 to the substrate Fe\/H2<\/sub>O2<\/sub> intermediate and then from the propionate C\u03b2-H to Tyr-145\u2022<\/sup>.<\/p>\n","protected":false},"excerpt":{"rendered":"DOI: 10.1074\/jbc.ra117.000830 Authors: Bennett R. Streit, Arianna I. Celis, Garrett C. Moraski, Krista A. Shisler, Eric M. Shepard, Kenton R. Rodgers, Gudrun S. Lukat-Rodgers, Jennifer L. DuBois Abstract: The H2O2-dependent oxidative decarboxylation of coproheme III is the final step in the biosynthesis of heme b in many microbes. However, the coproheme decarboxylase reaction mechanism is […]<\/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-547","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\/547","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=547"}],"version-history":[{"count":0,"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=\/wp\/v2\/posts\/547\/revisions"}],"wp:attachment":[{"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=547"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=547"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=547"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}