Haloferax denitrificans

The nitrate reductase from Haloferax denitrificans was purified to electrophoretic homogeneity aided by the ease with which the enzyme is solubilized from membranes and the stability of the reductase in solutions of low ionic strength [142]. The enzyme is composed of two subunits that resemble the a and (3 subunits of the dissimilatory nitrate reductases found in bacteria [143]. Dissimilatory nitrate reductases have a third subunit that contains a b-type cytochrome. No such subunit is detected in the nitrate reductase from H. denitrificans. However, this observation has no significance since this subunit is often lost during purification. The most striking property of the enzyme is its response to salt concentration, both when membrane-bound [144] and following purification [142]. Nitrate reduction is most active in the absence of added salt and the enzyme is stable for weeks on end in the absence of salt. Similar nitrate reductase activities occur in... 

There are two main types of NiRs involved in the reduction of nitrites, namely, the heme-containing cytochrome cdj NiR which was obtained and first purified from Thiosphaera pantotropha (261). The second kind of NiR is the copper-containing NiR which was first isolated from Alcaligenes xylosoxidans NCIB 11015, a bacterial isolated from a soil in Japan. Other Cu NiR have been isolated from, Achromohacter cycloclastes, Alcaligenes faecalis S-6, Bacillus halodenitrificans, Haloferax denitrificans, Nitrosomonas europaea, Pseudomonas aureofaciens, Rhodobacter sphaeroides, and Hyphomicrobium sp. (262 and references thereinj. In mammalian systems, nitrites are reduced by deoxyHb (263) and by ferrous myoglobin (264,265) to nitric oxide. In synthetic iron porphyrins. Ford and coworkers have demonstrated how nitrites inhibit the reductive nitrosylation process by forming ferric-nitrites species (266). 

CioH,6N207 276.246 Constit. of the O-specific polysaccharide of Pseudomonas aeruginosa strain 170014(serotype 06). Also from Haloferax denitrificans and Vibrio cholerae polysac-charidea... 

Among the haloarchaea, Haloferax and Haloarcula are studied extensively for production of EPS. Haloferax mediterranei was the first haloar-chaeon to be reported for EPS. The organism is isolated from Mediterranean Sea. The EPS has complex chemical composition and can be used in oil recovery especially in oil deposits with high salinity (Anton et al., 1988 Parolis et al., 1996). Acidic EPS produced by Haloferax denitrificans has been described by Parolis et al. (1999) and EPS of Haloferax gibbonsii by Paramonov et al. (1998). Nicolaus et al. (1999) have described EPS producing Haloarcula japonica strain T5, Haloarcula sp. strain T6 and strain T7. The information on halophiles producing EPS is summarized in Table 1.2. 

EPS production is not that common among Archaea, however, the halophilic Haloferax and Haloarcula and thermophilic Thermococcus are examples of producer genera. Whereas Haloferax gibbonsii and Haloferax denitrificans ate known to produce a neutral and an acidic EPS, respectively, sulfated EPSs have been isolated from Haloferax mediterranei and Haloarcula Japonica [44]. EPS production by the hyperthermophilic archaeon Thermococcus litoralis has been reported by Rinker and Kelly (2000). 

Haloarcula marismortui A5], Haloferax meditermnei, and another extreme halophile, strain Baja-12, chemotaxonomically identified as a member of the genus Haloferax [146]. The enzyme activities from these organisms are stable as well as most active in the absence of salt and the enzymatic properties are indistinguishable from those of H. denitrificans[HA]. 

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