TAILIEUCHUNG - Báo cáo khoa học: Molecular basis for specificities of reactivating factors for adenosylcobalamin-dependent diol and glycerol dehydratases

Adenosylcobalamin-dependent diol and glycerol dehydratases are isofunc-tional enzymes and undergo mechanism-based inactivation by a physiologi-cal substrate glycerol during catalysis. Inactivated holoenzymes are reactivated by their own reactivating factors that mediate the ATP-depen-dent exchange of an enzyme-bound, damaged cofactor for free adenosylco-balamin through intermediary formation of apoenzyme. | ễFEBS Journal Molecular basis for specificities of reactivating factors for adenosylcobalamin-dependent diol and glycerol dehydratases Hideki Kajiura1 Koichi Mori1 Naoki Shibata2 and Tetsuo Toraya1 1 Department of Bioscience and Biotechnology Graduate Schoolof NaturalScience and Technology Okayama University Japan 2 Graduate Schoolof Life Science University of Hyogo Japan Keywords adenosylcobalamin coenzyme B12 diol dehydratase glycerol dehydratase reactivating factors Correspondence T. Toraya Department of Bioscience and Biotechnology Faculty of Engineering Okayama University Tsushima-naka Okayama 700-8530 Japan Fax 81 86 2518264 Tel 81 86 2518194 E-mail toraya@ Received 26 May 2007 revised 17 August 2007 accepted 29 August 2007 doi Adenosylcobalamin-dependent diol and glycerol dehydratases are isofunctional enzymes and undergo mechanism-based inactivation by a physiological substrate glycerol during catalysis. Inactivated holoenzymes are reactivated by their own reactivating factors that mediate the ATP-depen-dent exchange of an enzyme-bound damaged cofactor for free adenosylcobalamin through intermediary formation of apoenzyme. The reactivation takes place in two steps a ADP-dependent cobalamin release and b ATP-dependent dissociation of the resulting apoenzyme-reactivating factor complexes. The in vitro experiments with purified proteins indicated that diol dehydratase-reactivating factor DDR cross-reactivates the inactivated glycerol dehydratase whereas glycerol dehydratase-reactivating factor GDR did not cross-reactivate the inactivated diol dehydratase. We investigated the molecular basis of their specificities in vitro by using purified preparations of cognate and noncognate enzymes and reactivating factors. DDR mediated the exchange of glycerol dehydratase-bound cyanocobalamin for free adeninylpentylcobalamin whereas GDR cannot mediate the exchange of diol dehydratase-bound cyanocobalamin for free .

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