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Nitrate-related down-regulation of respiratory nitrate reductase from Bradyrhizobium sp. (Lupinus)

100%
Polcyn W.
|
2008
|
vol. 55
|
issue 4
761-766
EN
Previously, we showed that anaerobic induction of respiratory nitrate reductase (NR) activity in Bradyrhizobium sp. (Lupinus) USDA 3045 is strongly enhanced by nitrate or nitrite through de novo synthesis. Here, multiple NR-active soluble forms, ranging from 75 kDa to 190 kDa, were observed under anaerobic conditions. Electrophoretic activity band patterns differed depending on the level and the type of the N oxyanion added. The intensity of the membrane-bound NR activity band of 230 kDa changed with time along with consumption of 2 mM nitrate. It was associated with a parallel 5-fold increase and then 2-fold reduction in the amount of membrane-bound NR protein. In contrast, on 4 mM nitrate, the level of NR protein was much more stable, apparently due to slower nitrate depletion. Moreover, in cells anaerobically grown without nitrate addition, a 42-kDa derivative of NR degradation was immunodetected, which was not observed if nitrate was present in the medium. These findings suggest that the amount of the respiratory NR protein could be negatively regulated by endogenous proteases in relation to the level of nitrate available. It seems, therefore, that multiple native forms might be not different isoenzymes but immature complexes or derivatives of the enzyme protein turnover. This report adds to a modest list of bacterial enzymes apparently regulated by proteolysis, such as GS, MurAA, EnvA, GdhA, and MetA.
2
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Mass spectrometry identification of membrane-bound respiratory nitrate reductase from Bradyrhizobium sp. (Lupinus)

100%
Polcyn W.
|
2008
|
vol. 55
|
issue 4
753-760
EN
Respiratory nitrate reductase (NR) from Bradyrhizobium sp. (Lupinus) USDA 3045 has biochemical properties of the membrane-bound NR type. However, in the completely sequenced rhizobium genomes only genes for the periplasmic type of dissimilatory NR were found. Therefore purification and identification of the enzyme by tandem mass spectrometry (MS/MS) was undertaken. MS/MS spectra representing 149 unique tryptic peptides derived from purified 137-kDa subunit matched the NCBInr-deposited NarG sequences. MS/MS sequencing of two other SDS/PAGE bands (65- and 59-kDa) identified them as derivatives of the NarH-type protein. Applying additional validation criteria, 73% of the sequence of the NarG subunit (902 aa) and 52% of NarH sequence (266 aa) was assembled (UniProt KB acc. no. P85097 and P85098). This is the first unambiguous identification of an active NarGH-like NR in rhizobia. Moreover, arguments are provided here for the existence of a functional enzyme of this type also among other rhizobial species, basing on immunoblot screening and the presence of membrane-associated NR-active electrophoretic forms.
3
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Nitrate reduction and nitrogen fixation in symbiotic association Rhizobium - legumes.

51%
Luciński R., Polcyn W., Ratajczak L.
|
2002
|
vol. 49
|
issue 2
537-546
EN
The inhibitory effect of nitrate on nitrogenase activity in root nodules of legume plants has been known for a long time. The major factor inducing changes in nitrogenase activity is the concentration of free oxygen inside nodules. Oxygen availability in the infected zone of nodule is limited, among others, by the gas diffusion resistance in nodule cortex. The presence of nitrate may cause changes in the resistance to O2 diffusion. The aim of this paper is to review literature data concerning the effect of nitrate on the symbiotic association between rhizobia and legume plants, with special emphasis on nitrogenase activity. Recent advances indicate that symbiotic associations of Rhizobium strains characterized by a high nitrate reductase activity are less susceptible to inhibition by nitrate. A thesis may be put forward that dissimilatory nitrate reduction, catalyzed by bacteroid nitrate reductase, significantly facilitates the symbiotic function of bacteroids.
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