Heterotrimeric NADH-Oxidizing Methylenetetrahydrofolate Reductase from the Acetogenic Bacterium Acetobacterium woodii

摘要: ABSTRACT The methylenetetrahydrofolate reductase (MTHFR) of acetogenic bacteria catalyzes the reduction methylene-THF, which is highly exergonic with NADH as reductant. Therefore, enzyme was suggested to be involved in energy conservation by reducing ferredoxin via electron bifurcation, followed Na+ translocation Rnf complex. purified from Acetobacterium woodii and shown have an unprecedented subunit composition containing three subunits RnfC2, MetF, MetV. stable complex contained 2 flavin mononucleotides (FMN), 23.5 ± 1.2 Fe 24.5 1.5 S, fits well predicted six [4Fe4S] clusters MetV RnfC2. catalyzed NADH:methylviologen NADH:ferricyanide oxidoreductase activity but also methylene-tetrahydrofolate (THF) NADH:methylene-THF high (248 U/mg) not stimulated ferredoxin. Furthermore, ferredoxin, alone or presence methylene-THF NADH, never observed. MetF MetVF able catalyze methylene-THF-dependent oxidation could reduce using methyl viologen donor. MTHFR did reverse reaction, endergonic methyl-THF NAD+ acceptor, this reaction driven reduced However, addition protein fractions made coupled possible. Our data demonstrate that A. according following reaction: + → NAD+. differences compositions MTHFRs are discussed light their different functions. IMPORTANCE Energy bacterium involves a chemiosmotic mechanism involving Na+-translocating Na+-dependent F1Fo ATP synthase. All redox enzymes pathway been characterized except (MTHFR). Here we report purification woodii, has heterotrimeric structure. reduces NADH. Ferredoxin stimulate reaction; neither it oxidized Since last potential role metabolism now characterized, can propose quantitative bioenergetic scheme for acetogenesis H2 plus CO2 model acetogen woodii.