Enzymes are long established as extremely efficient catalysts. Here, we show that enzymes can also be extremely efficient electrocatalysts (catalysts of redox reactions at electrodes). Despite being ...large and electronically insulating through most of their volume, some enzymes, when attached to an electrode, catalyze electrochemical reactions that are otherwise extremely sluggish (even with the best synthetic catalysts) and require a large overpotential to achieve a useful rate. These enzymes produce high electrocatalytic currents, displayed in single bidirectional voltammetric waves that switch direction (between oxidation and reduction) sharply at the equilibrium potential for the substrate redox couple. Notoriously irreversible processes such as CO2 reduction are thereby rendered electrochemically reversible—a consequence of molecular evolution responding to stringent biological drivers for thermodynamic efficiency. Enzymes thus set high standards for the catalysts of future energy technologies.
This article outlines examples of where electrochemical investigations of electrocatalysis by proteins immobilised on an electrode reveal fundamental information about electron-proton coupling in ...catalysis and provide a new way to energise, control and observe multi-enzyme cascades.
The brain endothelium constitutes a barrier to the passive movement of substances from the blood into the cerebral microenvironment, and disruption of this barrier after a stroke or trauma has ...potentially fatal consequences. Reactive oxygen species (ROS), which are formed during these cerebrovascular accidents, have a key role in this disruption. ROS are formed constitutively by mitochondria and also by the activation of cell receptors that transduce signals from inflammatory mediators, e.g., activated phospholipase A
2 forms arachidonic acid that interacts with cyclooxygenase and lipoxygenase to generate ROS. Endothelial NADPH oxidase, activated by cytokines, also contributes to ROS. There is a surge in ROS following reperfusion after cerebral ischemia and the interaction of the signaling pathways plays a role in this. This review critically evaluates the literature and concludes that the ischemic penumbra is a consequence of the initial edema resulting from the ROS surge after reperfusion.
Why did Nature choose manganese to make oxygen? Armstrong, Fraser A
Philosophical transactions of the Royal Society of London. Series B. Biological sciences,
03/2008, Letnik:
363, Številka:
1494
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at potentials above 1 V, ultimately to a super-oxidized level that includes one Mn(V) or a Mn(IV)-oxyl radical. The latter
is powerfully oxidizing and provides the crucial ‘power stroke’ necessary to ...generate an O–O bond. This leaves a centre still
rich in Mn(IV), ensuring a rapid follow-through to O, and form robust mixed-valence poly-oxo clusters in which the Mn(IV)/Mn(III) ratio can be elevated, one electron at a time,
accumulating oxidizing potential and capacity. The OEC is a Mn, cluster that undergoes sequential oxidations by P680, become oxidized, so it provides an uncomplicated building unit for the oxygen-evolving centre (OEC). The intermediate oxidation
states Mn(III) and Mn(IV) are strongly complexed by O, behaves like a Group 2 element—it is mobile, weakly complexing, easily taken up by cells and redox-inactive in simple aqueous
media. Only in the presence of suitable ligands does Mn, ., This paper discusses the suitability of manganese for its function in catalysing the formation of molecular oxygen from water.
Manganese is an abundant element. In terms of its inherent properties, Mn has a particularly rich redox chemistry compared
with other d-block elements, with several oxidizing states accessible. The most stable-state Mn
Transport infrastructure is exposed to natural hazards all around the world. Here we present the first global estimates of multi-hazard exposure and risk to road and rail infrastructure. Results ...reveal that ~27% of all global road and railway assets are exposed to at least one hazard and ~7.5% of all assets are exposed to a 1/100 year flood event. Global Expected Annual Damages (EAD) due to direct damage to road and railway assets range from 3.1 to 22 billion US dollars, of which ~73% is caused by surface and river flooding. Global EAD are small relative to global GDP (~0.02%). However, in some countries EAD reach 0.5 to 1% of GDP annually, which is the same order of magnitude as national transport infrastructure budgets. A cost-benefit analysis suggests that increasing flood protection would have positive returns on ~60% of roads exposed to a 1/100 year flood event.
Multistep enzyme-catalyzed cascade reactions are highly efficient in nature due to the confinement and concentration of the enzymes within nanocompartments. In this way, rates are exceptionally high, ...and loss of intermediates minimised. Similarly, extended enzyme cascades trapped and crowded within the nanoconfined environment of a porous conducting metal oxide electrode material form the basis of a powerful way to study and exploit myriad complex biocatalytic reactions and pathways. One of the confined enzymes, ferredoxin-NADP
reductase, serves as a transducer, rapidly and reversibly recycling nicotinamide cofactors electrochemically for immediate delivery to the next enzyme along the chain, thereby making it possible to energize, control and observe extended cascade reactions driven in either direction depending on the electrode potential that is applied. Here we show as proof of concept the synthesis of aspartic acid from pyruvic acid or its reverse oxidative decarboxylation/deamination, involving five nanoconfined enzymes.
Bacterial formate hydrogenlyase complex McDowall, Jennifer S; Murphy, Bonnie J; Haumann, Michael ...
Proceedings of the National Academy of Sciences - PNAS,
09/2014, Letnik:
111, Številka:
38
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Significance The isolation of an active formate hydrogenlyase is a breakthrough in understanding the molecular basis of bacterial hydrogen production. For over 100 years, Escherichia coli has been ...known to evolve H ₂ when cultured under fermentative conditions. Glucose is metabolized to formate, which is then oxidized to CO ₂ with the concomitant reduction of protons to H ₂ by a single complex called formate hydrogenlyase, which had been genetically, but never biochemically, characterized. In this study, innovative molecular biology and electrochemical experiments reveal a hydrogenase enzyme with the unique ability to sustain H ₂ production even under high partial pressures of H ₂. Harnessing bacterial H ₂ production offers the prospect of a source of fully renewable H ₂ energy, freed from any dependence on fossil fuel.
Under anaerobic conditions, Escherichia coli can carry out a mixed-acid fermentation that ultimately produces molecular hydrogen. The enzyme directly responsible for hydrogen production is the membrane-bound formate hydrogenlyase (FHL) complex, which links formate oxidation to proton reduction and has evolutionary links to Complex I, the NADH:quinone oxidoreductase. Although the genetics, maturation, and some biochemistry of FHL are understood, the protein complex has never been isolated in an intact form to allow biochemical analysis. In this work, genetic tools are reported that allow the facile isolation of FHL in a single chromatographic step. The core complex is shown to comprise HycE (a NiFe hydrogenase component termed Hyd-3), FdhF (the molybdenum-dependent formate dehydrogenase-H), and three iron-sulfur proteins: HycB, HycF, and HycG. A proportion of this core complex remains associated with HycC and HycD, which are polytopic integral membrane proteins believed to anchor the core complex to the cytoplasmic side of the membrane. As isolated, the FHL complex retains formate hydrogenlyase activity in vitro. Protein film electrochemistry experiments on Hyd-3 demonstrate that it has a unique ability among NiFe hydrogenases to catalyze production of H ₂ even at high partial pressures of H ₂. Understanding and harnessing the activity of the FHL complex is critical to advancing future biohydrogen research efforts.
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