Corrigendum to "Transport limited adsorption experiments give a new lower estimate of the turnover frequency of hydrogenase 1" BBA Advances 3 (2023) 100090.

[This corrects the article DOI: 10.1016/j.bbadva.

A Chimeric NiFe Hydrogenase Heterodimer to Assess the Role of the Electron Transfer Chain in Tuning the Enzyme's Catalytic Bias and Oxygen Tolerance.

The observation that some homologous enzymes have the same active site but very different catalytic properties demonstrates the importance of long-range effects in enzyme catalysis, but these effects are often difficult to rationalize. The NiFe hydrogenases 1 and 2 (Hyd 1 and Hyd 2) from both consist of a large catalytic subunit that embeds the same dinuclear active site and a small electron-transfer subunit with a chain of three FeS clusters. Hyd 1 is mostly active in H oxidation and resistant to inhibitors, whereas Hyd 2 also catalyzes H production and is strongly inhibited by O and CO.

Transport limited adsorption experiments give a new lower estimate of the turnover frequency of hydrogenase 1.

Protein Film Electrochemistry is a technique in which a redox enzyme is directly wired to an electrode, which substitutes for the natural redox partner. In this technique, the electrical current flowing through the electrode is proportional to the catalytic activity of the enzyme. However, in most cases, the amount of enzyme molecules contributing to the current is unknown and the absolute turnover frequency cannot be determined.

An essential role of the reversible electron-bifurcating hydrogenase Hnd for ethanol oxidation in .

The tetrameric cytoplasmic FeFe hydrogenase Hnd from (formely ) catalyses H oxidation and couples the exergonic reduction of NAD to the endergonic reduction of a ferredoxin by using a flavin-based electron-bifurcating mechanism. Regarding its implication in the bacterial physiology, we previously showed that Hnd, which is non-essential when bacteria grow fermentatively on pyruvate, is involved in ethanol metabolism. Under these conditions, it consumes H to produce reducing equivalents for ethanol production as a fermentative product.

NMR-based metabolomic analysis of the physiological role of the electron-bifurcating FeFe-hydrogenase Hnd in Solidesulfovibrio fructosivorans under pyruvate fermentation.

Solidesulfovibrio fructosivorans (formely Desulfovibrio fructosovorans), an anaerobic sulfate-reducing bacterium, possesses six gene clusters encoding six hydrogenases catalyzing the reversible oxidation of hydrogen gas (H) into protons and electrons. One of these, named Hnd, was demonstrated to be an electron-bifurcating hydrogenase Hnd (Kpebe et al., 2018).

The electron-bifurcating FeFe-hydrogenase Hnd is involved in ethanol metabolism in Desulfovibrio fructosovorans grown on pyruvate.

Desulfovibrio fructosovorans, a sulfate-reducing bacterium, possesses six gene clusters encoding six hydrogenases catalyzing the reversible oxidation of H into protons and electrons. Among them, Hnd is an electron-bifurcating hydrogenase, coupling the exergonic reduction of NAD to the endergonic reduction of a ferredoxin with electrons derived from H . It was previously hypothesized that its biological function involves the production of NADPH necessary for biosynthetic purposes.

Electrochemical Characterization of a Complex FeFe Hydrogenase, the Electron-Bifurcating Hnd From .

Hnd, an FeFe hydrogenase from , is a tetrameric enzyme that can perform flavin-based electron bifurcation. It couples the oxidation of H to both the exergonic reduction of NAD and the endergonic reduction of a ferredoxin. We previously showed that Hnd retains activity even when purified aerobically unlike other electron-bifurcating hydrogenases.

Overproduction of the Flv3B flavodiiron, enhances the photobiological hydrogen production by the nitrogen-fixing cyanobacterium Nostoc PCC 7120.

Background: The ability of some photosynthetic microorganisms, particularly cyanobacteria and microalgae, to produce hydrogen (H) is a promising alternative for renewable, clean-energy production. However, the most recent, related studies point out that much improvement is needed for sustainable cyanobacterial-based H production to become economically viable. In this study, we investigated the impact of induced O-consumption on H photoproduction yields in the heterocyte-forming, N-fixing cyanobacterium Nostoc PCC7120.

Hydrogenases and H metabolism in sulfate-reducing bacteria of the Desulfovibrio genus.

Hydrogen metabolism plays a central role in sulfate-reducing bacteria of the Desulfovibrio genus and is based on hydrogenases that catalyze the reversible conversion of protons into dihydrogen. These metabolically versatile microorganisms possess a complex hydrogenase system composed of several enzymes of both [FeFe]- and [NiFe]-type that can vary considerably from one Desulfovibrio species to another. This review covers the molecular and physiological aspects of hydrogenases and H metabolism in Desulfovibrio but focuses particularly on our model bacterium Desulfovibrio fructosovorans.

A new mechanistic model for an O-protected electron-bifurcating hydrogenase, Hnd from Desulfovibrio fructosovorans.

The genome of the sulfate-reducing and anaerobic bacterium Desulfovibrio fructosovorans encodes different hydrogenases. Among them is Hnd, a tetrameric cytoplasmic [FeFe] hydrogenase that has previously been described as an NADP-specific enzyme (Malki et al., 1995).

Clostridial whole cell and enzyme systems for hydrogen production: current state and perspectives.

Strictly anaerobic bacteria of the Clostridium genus have attracted great interest as potential cell factories for molecular hydrogen production purposes. In addition to being a useful approach to this process, dark fermentation has the advantage of using the degradation of cheap agricultural residues and industrial wastes for molecular hydrogen production. However, many improvements are still required before large-scale hydrogen production from clostridial metabolism is possible.

On the Natural History of Flavin-Based Electron Bifurcation.

Electron bifurcation is here described as a special case of the continuum of electron transfer reactions accessible to two-electron redox compounds with redox cooperativity. We argue that electron bifurcation is foremost an electrochemical phenomenon based on (a) strongly inverted redox potentials of the individual redox transitions, (b) a high endergonicity of the first redox transition, and (c) an escapement-type mechanism rendering completion of the first electron transfer contingent on occurrence of the second one. This mechanism is proposed to govern both the traditional quinone-based and the newly discovered flavin-based versions of electron bifurcation.

Phototrophic hydrogen production from a clostridial [FeFe] hydrogenase expressed in the heterocysts of the cyanobacterium Nostoc PCC 7120.

The conversion of solar energy into hydrogen represents a highly attractive strategy for the production of renewable energies. Photosynthetic microorganisms have the ability to produce H from sunlight but several obstacles must be overcome before obtaining a sustainable and efficient H production system. Cyanobacteria harbor [NiFe] hydrogenases required for the consumption of H.

Expression of terminal oxidases under nutrient-starved conditions in Shewanella oneidensis: detection of the A-type cytochrome c oxidase.

Shewanella species are facultative anaerobic bacteria that colonize redox-stratified habitats where O2 and nutrient concentrations fluctuate. The model species Shewanella oneidensis MR-1 possesses genes coding for three terminal oxidases that can perform O2 respiration: a bd-type quinol oxidase and cytochrome c oxidases of the cbb3-type and the A-type. Whereas the bd- and cbb3-type oxidases are routinely detected, evidence for the expression of the A-type enzyme has so far been lacking.

The aerobic respiratory chain of the acidophilic archaeon Ferroplasma acidiphilum: A membrane-bound complex oxidizing ferrous iron.

The extremely acidophilic archaeon Ferroplasma acidiphilum is found in iron-rich biomining environments and is an important micro-organism in naturally occurring microbial communities in acid mine drainage. F. acidiphilum is an iron oxidizer that belongs to the order Thermoplasmatales (Euryarchaeota), which harbors the most extremely acidophilic micro-organisms known so far.

A biochemical approach to study the role of the terminal oxidases in aerobic respiration in Shewanella oneidensis MR-1.

The genome of the facultative anaerobic γ-proteobacterium Shewanella oneidensis MR-1 encodes for three terminal oxidases: a bd-type quinol oxidase and two heme-copper oxidases, a A-type cytochrome c oxidase and a cbb 3-type oxidase. In this study, we used a biochemical approach and directly measured oxidase activities coupled to mass-spectrometry analysis to investigate the physiological role of the three terminal oxidases under aerobic and microaerobic conditions. Our data revealed that the cbb 3-type oxidase is the major terminal oxidase under aerobic conditions while both cbb 3-type and bd-type oxidases are involved in respiration at low-O2 tensions.

H₂-dependent azoreduction by Shewanella oneidensis MR-1: involvement of secreted flavins and both [Ni-Fe] and [Fe-Fe] hydrogenases.

In this paper, the hydrogen (H2)-dependent discoloration of azo dye amaranth by Shewanella oneidensis MR-1 was investigated. Experiments with hydrogenase-deficient strains demonstrated that periplasmic [Ni-Fe] hydrogenase (HyaB) and periplasmic [Fe-Fe] hydrogenase (HydA) are both respiratory hydrogenases of dissimilatory azoreduction in S. oneidensis MR-1.

The elusive third subunit IIa of the bacterial B-type oxidases: the enzyme from the hyperthermophile Aquifex aeolicus.

The reduction of molecular oxygen to water is catalyzed by complicated membrane-bound metallo-enzymes containing variable numbers of subunits, called cytochrome c oxidases or quinol oxidases. We previously described the cytochrome c oxidase II from the hyperthermophilic bacterium Aquifex aeolicus as a ba(3)-type two-subunit (subunits I and II) enzyme and showed that it is included in a supercomplex involved in the sulfide-oxygen respiration pathway. It belongs to the B-family of the heme-copper oxidases, enzymes that are far less studied than the ones from family A.

Original design of an oxygen-tolerant [NiFe] hydrogenase: major effect of a valine-to-cysteine mutation near the active site.

Hydrogenases are efficient biological catalysts of H(2) oxidation and production. Most of them are inhibited by O(2), and a prerequisite for their use in biotechnological applications under air is to improve their oxygen tolerance. We have previously shown that exchanging the residue at position 74 in the large subunit of the oxygen-sensitive [NiFe] hydrogenase from Desulfovibrio fructosovorans could impact the reaction of the enzyme with O(2) (Dementin, S.

New functional sulfide oxidase-oxygen reductase supercomplex in the membrane of the hyperthermophilic bacterium Aquifex aeolicus.

Aquifex aeolicus, a hyperthermophilic and microaerophilic bacterium, obtains energy for growth from inorganic compounds alone. It was previously proposed that one of the respiratory pathways in this organism consists of the electron transfer from hydrogen sulfide (H(2)S) to molecular oxygen. H(2)S is oxidized by the sulfide quinone reductase, a membrane-bound flavoenzyme, which reduces the quinone pool.

In vivo production of catalase containing haem analogues.

Haem (protohaem IX) analogues are toxic compounds and have been considered for use as antibacterial agents, but the primary mechanism behind their toxicity has not been demonstrated. Using the haem protein catalase in the Gram-positive bacterium Enterococcus faecalis as an experimental system, we show that a variety of haem analogues can be taken up by bacterial cells and incorporated into haem-dependent enzymes. The resulting cofactor-substituted proteins are dysfunctional, generally resulting in arrested cell growth or death.

Immobilization of the hyperthermophilic hydrogenase from Aquifex aeolicus bacterium onto gold and carbon nanotube electrodes for efficient H2 oxidation.

The electrochemistry of membrane-bound [NiFe] hydrogenase I ([NiFe]-hase I) from the hyperthermophilic bacterium Aquifex aeolicus was investigated at gold and graphite electrodes. Direct and mediated H(2) oxidation were proved to be efficient in a temperature range of 25-70 degrees C, describing a potential window for H(2) oxidation similar to that of O(2)-tolerant hydrogenases. Search for enhancement of current densities and enzyme stability was achieved by the use of carbon nanotube coatings.

A new iron-oxidizing/O2-reducing supercomplex spanning both inner and outer membranes, isolated from the extreme acidophile Acidithiobacillus ferrooxidans.

The iron respiratory chain of the acidophilic bacterium Acidithiobacillus ferrooxidans involves various metalloenzymes. Here we demonstrate that the oxygen reduction pathway from ferrous iron (named downhill pathway) is organized as a supercomplex constituted of proteins located in the outer and inner membranes as well as in the periplasm. For the first time, the outer membrane-bound cytochrome c Cyc2 was purified, and we showed that it is responsible for iron oxidation and determined that its redox potential is the highest measured to date for a cytochrome c.

Biocatalysts for fuel cells: efficient hydrogenase orientation for H2 oxidation at electrodes modified with carbon nanotubes.

We report the modification of gold and graphite electrodes with commercially available carbon nanotubes for immobilization of Desulfovibrio fructosovorans [NiFe] hydrogenase, for hydrogen evolution or consumption. Multiwalled carbon nanotubes, single-walled carbon nanotubes (SWCNs), and amine-modified and carboxyl-functionalized SWCNs were used and compared throughout. Two separate methods were performed: covalent attachment of oriented hydrogenase by controlled architecture of carbon nanotubes at gold electrodes, and adsorption of hydrogenase at carbon-nanotube-coated pyrolytic graphite electrodes.