tailieunhanh - Báo cáo khoa học: Reaction mechanisms of thiamin diphosphate enzymes: redox reactions

Amongst a wide variety of different biochemical reactions in cellular car-bon metabolism, thiamin diphosphate-dependent enzymes catalyze the oxi-dative decarboxylation of 2-keto acids. This type of reaction typically involves redox coupled acyl transfer to CoA or phosphate and is mediated by additional cofactors, such as flavins, iron-sulfur clusters or lipoamide swinging arms, which transmit the reducing equivalents that arise during keto acid oxidation to a final electron acceptor. | ễFEBS Journal MINIREVIEW Reaction mechanisms of thiamin diphosphate enzymes redox reactions Kai Tittmann Albrecht-von-Haller-Institut fur Pflanzenwissenschaften und Gottinger Zentrum fur Molekulare Biowissenschaften Georg-August-Universitat Gottingen Germany Keywords electron transfer flavin intermediate iron-sulfur cluster lipoamide oxidative decarboxylation phosphorolysis pyruvate radical X-ray crystallography Correspondence K. Tittmann Albrecht-von-Haller-Institut fcjr Pflanzenwissenschaften und Gottinger Zentrum fcjr Molekulare Biowissenschaften Georg-August-Universitat Gottingen Ernst-Caspari-Haus Justus-von-Liebig-Weg 11 D-37077 Gottingen Germany Fax 49 551 39 5749 Tel 49 551 39 14430 E-mail ktittma@ Received 7 November 2008 revised 3 February 2009 accepted 13 February 2009 doi Amongst a wide variety of different biochemical reactions in cellular carbon metabolism thiamin diphosphate-dependent enzymes catalyze the oxidative decarboxylation of 2-keto acids. This type of reaction typically involves redox coupled acyl transfer to CoA or phosphate and is mediated by additional cofactors such as flavins iron-sulfur clusters or lipoamide swinging arms which transmit the reducing equivalents that arise during keto acid oxidation to a final electron acceptor. EPR spectroscopic and kinetic studies have implicated the intermediacy of radical cofactor intermediates in pyruvate ferredoxin oxidoreductase and an acetyl phos-phate-producing pyruvate oxidase whereas the occurrence of transient on-pathway radicals in other enzymes is less clear. The structures of pyru-vate ferredoxin oxidoreductase and pyruvate oxidase with different enzymic reaction intermediates along the pathway including a radical intermediate were determined by cryo-crystallography and used to infer electron tunneling pathways and the potential roles of CoA and phosphate for an intimate coupling of electron and acyl group transfer. Viable mechanisms of reductive .