Application of hydrogenase in biotechnological conversions

Inhaled Gases as Therapies for Post-Cardiac Arrest Syndrome: A Narrative Review of Recent Developments

Despite recent advances in the management of post-cardiac arrest syndrome (PCAS), the survival rate, without neurologic sequelae after resuscitation, remains very low. Whole-body ischemia, followed by reperfusion after cardiac arrest (CA), contributes to PCAS, for which established pharmaceutical interventions are still lacking. It has been shown that a number of different processes can ultimately lead to neuronal injury and cell death in the pathology of PCAS, including vasoconstriction, protein modification, impaired mitochondrial respiration, cell death signaling, inflammation, and excessive oxidative stress. Recently, the pathophysiological effects of inhaled gases including nitric oxide (NO), molecular hydrogen (H₂), and xenon (Xe) have attracted much attention. Herein, we summarize recent literature on the application of NO, H₂, and Xe for treating PCAS. Recent basic and clinical research has shown that these gases have cytoprotective effects against PCAS. Nevertheless, there are likely differences in the mechanisms by which these gases modulate reperfusion injury after CA. Further preclinical and clinical studies examining the combinations of standard post-CA care and inhaled gas treatment to prevent ischemia-reperfusion injury are warranted to improve outcomes in patients who are being failed by our current therapies.

Molecular hydrogen as a novel antioxidant: overview of the advantages of hydrogen for medical applications

Molecular hydrogen (H2) was believed to be inert and nonfunctional in mammalian cells. We overturned this concept by demonstrating that H2 reacts with highly reactive oxidants such as hydroxyl radical ((•)OH) and peroxynitrite (ONOO(-)) inside cells. H2 has several advantages exhibiting marked effects for medical applications: it is mild enough neither to disturb metabolic redox reactions nor to affect signaling by reactive oxygen species. Therefore, it should have no or little adverse effects. H2 can be monitored with an H2-specific electrode or by gas chromatography. H2 rapidly diffuses into tissues and cells to exhibit efficient effects. Thus, we proposed the potential of H2 for preventive and therapeutic applications. There are several methods to ingest or consume H2: inhaling H2 gas, drinking H2-dissolved water (H2-water), injecting H2-dissolved saline (H2-saline), taking an H2 bath, or dropping H2-saline onto the eyes. Recent publications revealed that, in addition to the direct neutralization of highly reactive oxidants, H2 indirectly reduces oxidative stress by regulating the expression of various genes. Moreover, by regulating gene expression, H2 functions as an anti-inflammatory, antiallergic, and antiapoptotic molecule, and stimulates energy metabolism. In addition to growing evidence obtained by model animal experiments, extensive clinical examinations were performed or are under way. Since most drugs specifically act on their specific targets, H2 seems to differ from conventional pharmaceutical drugs. Owing to its great efficacy and lack of adverse effects, H2 has potential for clinical applications for many diseases.

H₂-driven cofactor regeneration with NAD(P)⁺-reducing hydrogenases

A large number of industrially relevant enzymes depend upon nicotinamide cofactors, which are too expensive to be added in stoichiometric amounts. Existing NAD(P)H-recycling systems suffer from low activity, or the generation of side products. H₂-driven cofactor regeneration has the advantage of 100% atom efficiency and the use of H₂ as a cheap reducing agent, in a world where sustainable energy carriers are increasingly attractive. The state of development of H₂-driven cofactor-recycling systems and examples of their integration with enzyme reactions are summarized in this article. The O₂-tolerant NAD⁺-reducing hydrogenase from Ralstonia eutropha is a particularly attractive candidate for this approach, and we therefore discuss its catalytic properties that are relevant for technical applications.

[NiFe] hydrogenases: a common active site for hydrogen metabolism under diverse conditions

Hydrogenase proteins catalyze the reversible conversion of molecular hydrogen to protons and electrons. The most abundant hydrogenases contain a [NiFe] active site; these proteins are generally biased towards hydrogen oxidation activity and are reversibly inhibited by oxygen. However, there are [NiFe] hydrogenase that exhibit unique properties, including aerobic hydrogen oxidation and preferential hydrogen production activity; these proteins are highly relevant in the context of biotechnological devices. This review describes four classes of these "nonstandard" [NiFe] hydrogenases and discusses the electrochemical, spectroscopic, and structural studies that have been used to understand the mechanisms behind this exceptional behavior. A revised classification protocol is suggested in the conclusions, particularly with respect to the term "oxygen-tolerance". This article is part of a special issue entitled: metals in bioenergetics and biomimetics systems.

Microsomal preparations from plant and yeast acylate free fatty acids without prior activation to acyl-thioesters

Acylation of fatty acids to hydroxy groups in cells generally require activation to a thioester (ACP or CoA) or transacylation from another oxygen ester. We now show that microsomal membranes from Arabidopsis leaves efficiently acylate free fatty acids to long chain alcohols with no activation of the fatty acids to thioesters prior to acylation. Studies of the fatty alcohol and fatty acids specificities of the reaction in membranes from Arabidopsis leaves revealed that long chain (C18-C24) unsaturated fatty alcohols and C18-C22 unsaturated fatty acids were preferred. Microsomal preparations from Arabidopsis roots and leaves and from yeast efficiently synthesized ethyl esters from ethanol and free fatty acids. This reaction also occurred without prior activation of the fatty acid to a thioester. The results presented strongly suggest that wax ester and ethyl ester formation are carried out by separate enzymes. The physiological significance of the reactions in plants is discussed in connection to suberin and cutin synthesis. The results also have implication regarding the interpretation of lipid metabolic experiments done with microsomal fraction.

Evaluation of Alcaligenes eutrophus cells as an NADH regenerating catalyst in organic-aqueous two-phase system

A soluble NAD-dependent hydrogenase contained in Alcaligenes eutrophus was evaluated as a coenzyme regenerating catalyst in an organic-aqueous two-phase (predominantly organic) system. The horse-liver alcohol-dehydrogenase (HLADH) catalyzed reduction of cyclohexanone to cyclohexanol was used as a model reaction. The impact of different solvents (selected to span a large variety of principal properties) on the stability and activity of the HLADH, using substrate-driven regeneration, was studied. Solvents suitable for the HLADH were then selected for an evaluation of the hydrogenase-driven coenzyme regeneration. Hydrophobic solvents such as heptane, toluene, and 1,1,1-trichloroethane were found to be suitable for the coupled reactions catalyzed by HLADH and hydrogenase. Nonimmobilized cells, permeabilized with cetyl-trimethyl-ammonium bromide, were the most efficient preparation for the regeneration of NADH. The use of this preparation in heptane (10% water) was optimized with respect to the yield obtained in the HLADH-catalyzed reduction of cyclohexanone. Using the optimized conditions, yields of 99% cyclohexanol were obtained.

Kinetic models in reverse micelles

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Enzymatic catalysts in organic synthesis

The synthetic value of enzymes is being increasingly recognized. With an understanding of enzyme-catalyzed reactions and the techniques now available for the low-cost production and rational alteration of enzymes and for the design of new enzymatic activities, biocatalytic synthesis should become one of the most valuable synthetic methods. The fundamental as well as the practical issues of this rapidly growing area are described and its impact on the technology pertaining to synthesis is considered.

Redox-dependent inactivation of the NAD-dependent hydrogenase from Alcaligenes eutrophus Z1

A novel inactivation mechanism of the NAD-dependent hydrogenase from Alcaligenes eutrophus Z1 comprising redox-dependent steps is described. The model of the hydrogenase inactivation process is proposed which implies that the enzyme may exist in several forms which differ in their stability and spectral properties. One of these forms, existing within a limited (approximately -200 +/- 30 mV) potential range, undergoes a rapid and irreversible inactivation. The dissociation of the FMN prosthetic group from the apohydrogenase appears to be the main reason for the enzyme inactivation. The rationale for the enzyme stabilization under real operational conditions based on the chemical modification of the hydrogenase molecule is suggested.