Anaerobic hydrogenase systems

Figure SJ Activity of the various states of the [NiFe] hydrogenase from A. vinosum as determined with a Pt electrode at 30°C.The reaction was performed in SOmM Tris/HCI (pH 8.0) in a volume of 2 ml. Oxygen was scavenged by adding glucose (90 mM) and glucose oxidase (2.5 mg/ml). Hydrogen peroxide was removed by catalase. When the system was anaerobic, an aliquot of H2-saturated water was added, and a little later enzyme (S-IOnM) was injected. Benzyl viologen (4.2mM) was used as electron acceptor.

This review describes our unique assay system to investigate the role of cell-free hydrogenases in anaerobic biocorrosion, which resulted in proposing a new biocorrosion model. 

Several selenoproteins have been found in certain bacteria and archaea. A hydrogenase from Methano-coccus vannielii contains selenocysteine.559 560 This enzyme transfers electrons from H2 to the C-5 si face of the 8-hydroxy-5-deazaflavin cofactor F q (Section B,4). The same bacterium synthesizes two formate dehydrogenases (see Fig 15-23), one of which contains Se. Two Se-containing formate dehydrogenases are made by E. coli. One of them, which is coupled to a hydrogenase in the formate hydrogen-lyase system (see Eq. 15-37), is a 715-residue protein containing selenocysteine at position 140.561-563 The second has selenocysteine at position 196 and functions with a nitrate reductase in anaerobic nitrate respiration.561... 

Overall, the rates of H2-production in the system are limited by the rates of electron transport from the H20-oxidizing complex to hydrogenase under anaerobic conditions. H2-production during sulfur-deprivation provides the means to reactivate residual photosynthetic electron transport capacity, which is rapidly down-regulated by the establishment of anaerobiosis. 

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