Enzymes hydrogenases

It can be seen from equation 2.14 that the ratio of iron corroded to iron in the form of sulphide should be 4 1, but values from 0.9 to 48 are commonly obtained experimentally. Subsequently it was shown by Booth and his co-workers that the ratios of the corrosion products were dependent on the particular strain of Desulphovibrio and on their rates of growth. Later the activity of the enzyme hydrogenase which bring about the reaction ... 

In contrast to the abundance of Fe-proteins, there are only six known nickel-containing enzymes hydrogenase, CO dehydrogenase (CODA), acetyl-CoA synthase (ACS), superoxide dismutase, urease, and S-methyl-CoM methylreductase. Among these enzymes, it exists in very diverse environments, including a dinickel site (urease), a Ni-Fe heterobinuclear site (hydrogenase), a Ni-Fe4S4 heterometallic... 

Sulfate reducing bacteria of the genus Desulfovibrio are one of the main sources of enzyme. Hydrogenases can be found in different sites in the bacterial cell periplasm, cytoplasm, and membrane. A given species may have hydrogenases in one or in several of these cell sites. 

The enzymes hydrogenase, nitrogenase, and formate dehydrogenase can be used to equilibrate reducing reagents with H2O/H2, N2NH3, and CO2/HCOOH, respectively.(53) In no case do the enzymes involve expensive noble metals as catalysts. 

A. A. Karyakin, S. V. Morozov, E. E. Karyakina, S. D. Varfolomeyev, N. A. Zorin, S. Cosnier (2002) Hydrogen fuel electrode based on bioelectrocatalysis by enzyme hydrogenase. Electrochem. Commun., 4 417-420... 

M. Klibanov (1983) Biotechnological potential of the enzyme hydrogenase. Process Biochem, 18 13-16... 

The key enzyme hydrogenase catalyses the reversible reduction of protons to molecular hydrogen. Inhibitor experiments indicate that the ferredoxin PetF functions as natural electron donor linking the hydrogenase to the photosynthetic electron transport chain [Florin et al., 2001],... 

Usually, activities of enzymes (hydrogenases included) are investigated in solutions with water as the solvent. However, enhancement of enzyme activity is sometimes described for non-aqueous or water-limiting surroundings, particular for hydrophobic (or oily) substrates. Ternary phase systems such as water-in-oil microemulsions are useful tools for investigations in this field. Microemulsions are prepared by dispersion of small amounts of water and surfactant in organic solvents. In these systems, small droplets of water (l-50nm in diameter) are surrounded by a monolayer of surfactant molecules (Fig. 9.15). The water pool inside the so-called reverse micelle represents a combination of properties of aqueous and non-aqueous environments. Enzymes entrapped inside reverse micelles depend in their catalytic activity on the size of the micelle, i.e. the water content of the system (at constant surfactant concentrations). 

The enzyme hydrogenase (hydrogen dehydrogenase EC 1.12.1.2) is able to reduce electron acceptors by molecular hydrogen. When it is used in cofactor regenerating systems, consumed NADH can be regenerated directly by molecular hydrogen. 

The biochemical pathway of both assimilatory and dissimilatory sulfate reduction is illustrated in Figure 1. The details of the dissimilatory reduction pathway are useful for understanding the origin of bacterial stable isotopic fractionations. The overall pathways require the transfer of eight electrons, and proceed through a number of intermediate steps. The reduction of sulfate requires activation by ATP (adenosine triphosphate) to form adenosine phosphosulfate (APS). The enzyme ATP sulfurylase catalyzes this reaction. In dissimilatory reduction, the sulfate moiety of APS is reduced to sulfite (SO3 ) by the enzyme APS reductase, whereas in assimilatory reduction APS is further phosphorylated to phospho-adenosine phosphosulfate (PAPS) before reduction to the oxidation state of sulfite and sulfide. Although the reduction reactions occur in the cell s cytoplasm (i.e., the sulfate enters the cell), the electron transport chain for dissimilatory sulfate reduction occurs in proteins that are peiiplasmic (within the bacterial cell wall). The enzyme hydrogenase... 

Three of the eight Ni enzymes, hydrogenase, CO dehydrogenase (CODH), and acetyl-CoA synthase (ACS), are Ni—Fe—S proteins. Hydrogenases play an important role in microbial energy metabolism by catalysing the reversible oxidation of hydrogen ... 

In a recent review it has been pointed out that the most probable metal for the role of receptor site for hydrogen in the enzyme hydrogenase is either cobalt or iron ). It is therefore of particular interest to investigate the nature and properties of the hydrogenation catalyst which is formed when KCN is added to an aqueous solution of C0CI2 2). No iron complex is yet known which can react in solution with hydrogen gas. 

Biologically produced photohydrogen has been obtained using the unicellular green alga Scenedesmus The responsible enzyme hydrogenase must first be activated by anaerobic adaptation, and the process which involves coupling of... 

The reaction is catalyzed by an enzyme called Ferredoxin-NADP reductase FNR. If this enzyme is blocked, certain plants can produce gaseous hydrogen using the enzyme hydrogenase [218]. This is indeed used to produce hydrogen from algae and bacteria [219]. 

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