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Báo cáo khoa học: The occurrence of riboflavin kinase and FAD synthetase ensures FAD synthesis in tobacco mitochondria and maintenance of cellular redox status

Intact mitochondria isolated from Nicotiana tabacumcv. Bright Yellow 2 (TBY-2) cells can take up riboflavin via carrier-mediated systems that oper-ate at different concentration ranges and have different uptake efficiencies. Once inside mitochondria, riboflavin is converted into catalytically active cofactors, FMN and FAD, due to the existence of a mitochondrial ribofla-vin kinase (EC 2.7.1.26) and an FAD synthetase (EC 2.7.7.2). | The occurrence of riboflavin kinase and FAD synthetase ensures FAD synthesis in tobacco mitochondria and maintenance of cellular redox status Teresa A. Giancaspero1 Vittoria Locate2 Maria C. de Pinto3 Laura De Gara2 3 and Maria Barile1 1 Dipartimento di Biochimica e Biologia Molecolare E. Quagliariello University degli Studi di Bari Italy 2 Centro Interdipartimentale di Ricerche Biomediche CIR Universita Campus Biomedico Roma Italy 3 Dipartimento di Biologia e Patologia Vegetale Universita degli Studi di Bari Italy Keywords FAD synthetase flavin riboflavin kinase riboflavin transport TBY-2 mitochondria Correspondence M. Barile Dipartimento di Biochimica e Biologia Molecolare Quagliariello Universita degli Studi di Bari Via Orabona 4 I-70126 Bari Italy Fax 39 0805443317 Tel 39 0805443604 E-mail m.barile@biologia.uniba.it Received 11 August 2008 revised 30 October 2008 accepted 31 October 2008 doi 10.1111 j.1742-4658.2008.06775.x Intact mitochondria isolated from Nicotiana tabacum cv. Bright Yellow 2 TBY-2 cells can take up riboflavin via carrier-mediated systems that operate at different concentration ranges and have different uptake efficiencies. Once inside mitochondria riboflavin is converted into catalytically active cofactors FMN and FAD due to the existence of a mitochondrial riboflavin kinase EC 2.7.1.26 and an FAD synthetase EC 2.7.7.2 . Newly synthesized FAD can be exported from intact mitochondria via a putative FAD exporter. The dependence of FMN synthesis rate on riboflavin concentration shows saturation kinetics with a sigmoidal shape S0.5 Vmax and Hill coefficient values 0.32 0.12 M 1.4 nmol-min_1-mg_1 protein and 3.1 respectively . The FAD-forming enzymes are both activated by MgCl2 and reside in two distinct monofunctional enzymes which can be physically separated in mitochondrial soluble and membrane-enriched fractions respectively. Whereas mammals must obtain riboflavin Rf vitamin B2 from food plants along with fungi and bacteria can synthesize Rf