Methyl (Alkyl)-Coenzyme M Reductases: Nickel F-430-Containing Enzymes Involved in Anaerobic Methane Formation and in Anaerobic Oxidation of Methane or of Short Chain Alkanes.

Methyl-coenzyme M reductase (MCR) catalyzes the methane-forming step in methanogenic archaea. The active enzyme harbors the nickel(I) hydrocorphin coenzyme F-430 as a prosthetic group and catalyzes the reversible reduction of methyl-coenzyme M (CH-S-CoM) with coenzyme B (HS-CoM) to methane and CoM-S-S-CoB. MCR is also involved in anaerobic methane oxidation in reverse of methanogenesis and most probably in the anaerobic oxidation of ethane, propane, and butane.

Flavin-Based Electron Bifurcation, Ferredoxin, Flavodoxin, and Anaerobic Respiration With Protons (Ech) or NAD (Rnf) as Electron Acceptors: A Historical Review.

Flavin-based electron bifurcation is a newly discovered mechanism, by which a hydride electron pair from NAD(P)H, coenzyme FH, H, or formate is split by flavoproteins into one-electron with a more negative reduction potential and one with a more positive reduction potential than that of the electron pair. Via this mechanism microorganisms generate low- potential electrons for the reduction of ferredoxins (Fd) and flavodoxins (Fld). The first example was described in 2008 when it was found that the butyryl-CoA dehydrogenase-electron-transferring flavoprotein complex (Bcd-EtfAB) of couples the endergonic reduction of ferredoxin (E' = -420 mV) with NADH (-320 mV) to the exergonic reduction of crotonyl-CoA to butyryl-CoA (-10 mV) with NADH.

Flavin-Based Electron Bifurcation, A New Mechanism of Biological Energy Coupling.

There are two types of electron bifurcation (EB), either quinone- or flavin-based (QBEB/FBEB), that involve reduction of a quinone or flavin by a two-electron transfer and two reoxidations by a high- and low-potential one-electron acceptor with a reactive semiquinone intermediate. In QBEB, the reduced low-potential acceptor (cytochrome b) is exclusively used to generate ΔμH. In FBEB, the "energy-rich" low-potential reduced ferredoxin or flavodoxin has dual function.

Lothar Jaenicke and C1-metabolism: his first 25 years of research.

The biochemist Lothar Jaenicke died on 29 December 2015, aged 92 years old. The last time I saw him was at his 90th birthday on 14 September 2013, at the occasion of which his colleagues at the Universität zu Köln (Cologne) in Germany had organized a symposium to honor him.

Diversity of bacteria and archaea from two shallow marine hydrothermal vents from Vulcano Island.

To obtain new insights into community compositions of hyperthermophilic microorganisms, defined as having optimal growth temperatures of 80 °C and above, sediment and water samples were taken from two shallow marine hydrothermal vents (I and II) with temperatures of 100 °C at Vulcano Island, Italy. A combinatorial approach of denaturant gradient gel electrophoresis (DGGE) and metagenomic sequencing was used for microbial community analyses of the samples. In addition, enrichment cultures, growing anaerobically on selected polysaccharides such as starch and cellulose, were also analyzed by the combinatorial approach.

Energy in Ancient Metabolism.

Modern metabolism would not work without ATP and phosphate, but in primordial biochemical networks, energy currencies might have been simpler. Goldford et al. report a novel systems approach to reconstructing energetics in ancient metabolism, with very interesting results.

Mode of action uncovered for the specific reduction of methane emissions from ruminants by the small molecule 3-nitrooxypropanol.

Ruminants, such as cows, sheep, and goats, predominantly ferment in their rumen plant material to acetate, propionate, butyrate, CO2, and methane. Whereas the short fatty acids are absorbed and metabolized by the animals, the greenhouse gas methane escapes via eructation and breathing of the animals into the atmosphere. Along with the methane, up to 12% of the gross energy content of the feedstock is lost.

My Lifelong Passion for Biochemistry and Anaerobic Microorganisms.

Early parental influence led me first to medical school, but after developing a passion for biochemistry and sensing the need for a deeper foundation, I changed to chemistry. During breaks between semesters, I worked in various biochemistry labs to acquire a feeling for the different areas of investigation. The scientific puzzle that fascinated me most was the metabolism of the anaerobic bacterium Clostridium kluyveri, which I took on in 1965 in Karl Decker's lab in Freiburg, Germany.

Energy Conservation Associated with Ethanol Formation from H2 and CO2 in Clostridium autoethanogenum Involving Electron Bifurcation.

Unlabelled: Most acetogens can reduce CO2 with H2 to acetic acid via the Wood-Ljungdahl pathway, in which the ATP required for formate activation is regenerated in the acetate kinase reaction. However, a few acetogens, such as Clostridium autoethanogenum, Clostridium ljungdahlii, and Clostridium ragsdalei, also form large amounts of ethanol from CO2 and H2. How these anaerobes with a growth pH optimum near 5 conserve energy has remained elusive.

Insights into Flavin-based Electron Bifurcation via the NADH-dependent Reduced Ferredoxin:NADP Oxidoreductase Structure.

NADH-dependent reduced ferredoxin:NADP oxidoreductase (NfnAB) is found in the cytoplasm of various anaerobic bacteria and archaea. The enzyme reversibly catalyzes the endergonic reduction of ferredoxin with NADPH driven by the exergonic transhydrogenation from NADPH onto NAD(+). Coupling is most probably accomplished via the mechanism of flavin-based electron bifurcation.

Life under extreme energy limitation: a synthesis of laboratory- and field-based investigations.

The ability of microorganisms to withstand long periods with extremely low energy input has gained increasing scientific attention in recent years. Starvation experiments in the laboratory have shown that a phylogenetically wide range of microorganisms evolve fitness-enhancing genetic traits within weeks of incubation under low-energy stress. Studies on natural environments that are cut off from new energy supplies over geologic time scales, such as deeply buried sediments, suggest that similar adaptations might mediate survival under energy limitation in the environment.

Hydrogen formation and its regulation in Ruminococcus albus: involvement of an electron-bifurcating [FeFe]-hydrogenase, of a non-electron-bifurcating [FeFe]-hydrogenase, and of a putative hydrogen-sensing [FeFe]-hydrogenase.

Ruminococcus albus 7 has played a key role in the development of the concept of interspecies hydrogen transfer. The rumen bacterium ferments glucose to 1.3 acetate, 0.

Evidence for a hexaheteromeric methylenetetrahydrofolate reductase in Moorella thermoacetica.

Moorella thermoacetica can grow with H₂ and CO₂, forming acetic acid from 2 CO₂ via the Wood-Ljungdahl pathway. All enzymes involved in this pathway have been characterized to date, except for methylenetetrahydrofolate reductase (MetF). We report here that the M.

Methyl-coenzyme M reductase from methanogenic archaea: isotope effects on the formation and anaerobic oxidation of methane.

The nickel enzyme methyl-coenzyme M reductase (MCR) catalyzes two important transformations in the global carbon cycle: methane formation and its reverse, the anaerobic oxidation of methane. MCR uses the methyl thioether methyl-coenzyme M (CH3-S-CH2CH2-SO3(-), Me-S-CoM) and the thiol coenzyme B (CoB-SH) as substrates and converts them reversibly to methane and the corresponding heterodisulfide (CoB-S-S-CoM). The catalytic mechanism is still unknown.

Methyl-coenzyme M reductase from methanogenic archaea: isotope effects on label exchange and ethane formation with the homologous substrate ethyl-coenzyme M.

Ethyl-coenzyme M (CH3CH2-S-CH2CH2-SO3(-), Et-S-CoM) serves as a homologous substrate for the enzyme methyl-coenzyme M reductase (MCR) resulting in the product ethane instead of methane. The catalytic reaction proceeds via an intermediate that already contains all six C-H bonds of the product. Because product release occurs after a second, rate-limiting step, many cycles of intermediate formation and reconversion to substrate occur before a substantial amount of ethane is released.

NADP-specific electron-bifurcating [FeFe]-hydrogenase in a functional complex with formate dehydrogenase in Clostridium autoethanogenum grown on CO.

Flavin-based electron bifurcation is a recently discovered mechanism of coupling endergonic to exergonic redox reactions in the cytoplasm of anaerobic bacteria and archaea. Among the five electron-bifurcating enzyme complexes characterized to date, one is a heteromeric ferredoxin- and NAD-dependent [FeFe]-hydrogenase. We report here a novel electron-bifurcating [FeFe]-hydrogenase that is NADP rather than NAD specific and forms a complex with a formate dehydrogenase.

Clostridium acidurici electron-bifurcating formate dehydrogenase.

Cell extracts of uric acid-grown Clostridium acidurici catalyzed the coupled reduction of NAD(+) and ferredoxin with formate at a specific activity of 1.3 U/mg. The enzyme complex catalyzing the electron-bifurcating reaction was purified 130-fold and found to be composed of four subunits encoded by the gene cluster hylCBA-fdhF2.

A reversible electron-bifurcating ferredoxin- and NAD-dependent [FeFe]-hydrogenase (HydABC) in Moorella thermoacetica.

Moorella thermoacetica was long the only model organism used to study the biochemistry of acetogenesis from CO(2). Depending on the growth substrate, this Gram-positive bacterium can either form H(2) or consume it. Despite the importance of H(2) in its metabolism, a hydrogenase from the organism has not yet been characterized.

Energy conservation via electron bifurcating ferredoxin reduction and proton/Na(+) translocating ferredoxin oxidation.

The review describes four flavin-containing cytoplasmatic multienzyme complexes from anaerobic bacteria and archaea that catalyze the reduction of the low potential ferredoxin by electron donors with higher potentials, such as NAD(P)H or H(2) at ≤ 100 kPa. These endergonic reactions are driven by concomitant oxidation of the same donor with higher potential acceptors such as crotonyl-CoA, NAD(+) or heterodisulfide (CoM-S-S-CoB). The process called flavin-based electron bifurcation (FBEB) can be regarded as a third mode of energy conservation in addition to substrate level phosphorylation (SLP) and electron transport phosphorylation (ETP).

Electron bifurcation involved in the energy metabolism of the acetogenic bacterium Moorella thermoacetica growing on glucose or H2 plus CO2.

Moorella thermoacetica ferments glucose to three acetic acids. In the oxidative part of the fermentation, the hexose is converted to 2 acetic acids and 2 CO(2) molecules with the formation of 2 NADH and 2 reduced ferredoxin (Fd(red)(2-)) molecules. In the reductive part, 2 CO(2) molecules are reduced to acetic acid, consuming the 8 reducing equivalents generated in the oxidative part.

An ancient pathway combining carbon dioxide fixation with the generation and utilization of a sodium ion gradient for ATP synthesis.

Synthesis of acetate from carbon dioxide and molecular hydrogen is considered to be the first carbon assimilation pathway on earth. It combines carbon dioxide fixation into acetyl-CoA with the production of ATP via an energized cell membrane. How the pathway is coupled with the net synthesis of ATP has been an enigma.

Structure of a methyl-coenzyme M reductase from Black Sea mats that oxidize methane anaerobically.

The anaerobic oxidation of methane (AOM) with sulphate, an area currently generating great interest in microbiology, is accomplished by consortia of methanotrophic archaea (ANME) and sulphate-reducing bacteria. The enzyme activating methane in methanotrophic archaea has tentatively been identified as a homologue of methyl-coenzyme M reductase (MCR) that catalyses the methane-forming step in methanogenic archaea. Here we report an X-ray structure of the 280 kDa heterohexameric ANME-1 MCR complex.