TAILIEUCHUNG - Báo cáo khoa học: Re-evaluation of the function of the F420dehydrogenase in electron transport ofMethanosarcina mazei

Methanosarcina mazeiis a methanogenic archaeon that is able to thrive on various substrates and therefore contains a variety of redox-active proteins involved in both cytoplasmic and membrane-bound electron transport. The organism possesses a complex branched respiratory chain that has the abil-ity to utilize different electron donors. | IFEBS Journal Re-evaluation of the function of the F420 dehydrogenase in electron transport of Methanosarcina mazei Cornelia Welte and Uwe Deppenmeier Institute of Microbiology and Biotechnology University of Bonn Germany Keywords archaea electron transport energy conservation hydrogenase methane methanogenesis Correspondence U. Deppenmeier Institut fur Mikrobiologie und Biotechnologie University of Bonn Meckenheimer Allee 168 53115 Bonn Germany Fax 49 228 737576 Tel 49 228 735590 E-mail udeppen@ Received 2 December 2010 revised 14 January 2011 accepted 7 February 2011 doi Methanosarcina mazei is a methanogenic archaeon that is able to thrive on various substrates and therefore contains a variety of redox-active proteins involved in both cytoplasmic and membrane-bound electron transport. The organism possesses a complex branched respiratory chain that has the ability to utilize different electron donors. In this study two knockout mutants of the membrane-bound F420 dehydrogenase DfpoF and DfpoA-O were constructed and analyzed. They exhibited severe growth deficiencies with trimethylamine but not with acetate as substrates. In cell lysates of the fpo mutants the F420 heterodisulfide oxidoreductase activity was strongly reduced although soluble F420 hydrogenase was still present. This led to the conclusion that the predominant part of cellular oxidation of the reduced form of F420 F420H2 in Ms. mazei is performed by F420 dehydrogenase. Enzyme assays of cytoplasmic fractions revealed that ferredoxin Fd F420 oxidoreductase activity was essentially absent in the DfpoF mutant. Subsequently FpoF was produced in Escherichia coli and purified for further characterization. The purified FpoF protein catalyzed the Fd F420 oxidoreductase reaction with high specificity the KM for reduced Fd was M but with low velocity Vmax 225 mU-mg 1 and was present in the Ms. mazei cytoplasm in considerable amounts. Consequently soluble FpoF .

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