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Query: UMLS:C0031511 (pheochromocytoma)
 14,622 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Nitrate assimilation-defective mutants SP7, SP9, and SP17 of the cyanobacterium Anabaena sp. PCC 7120 were isolated by use of transposon mutagenesis and screened on medium containing chlorate. SP7 and SP17 represented nitrate reductase-defective nature, while mutant SP9 appeared to be a regulatory mutant exhibiting pleiotropic behavior. Kinetics of nitrate uptake system exhibited K(s) values of 31-38 &mgr;M for parent, SP7, and SP17 strains; however, mutant SP9 exhibited a high K(s) value of 109.5 &mgr;M. Defective nitrate reductase was apparent in mutant SP7 and SP9, while mutant SP17 exhibited partial defective nature. Methyl viologen-dependent NR activity in parent strain presented a biphasic nature with K(m) values of 0.13 and 2.47 mM, whereas a single K(m) value (2.96 mM) was observed for mutant SP17. Mutant SP9 was also defective in nitrite uptake and reduction. Mutant strains exhibited derepressed nitrogenase activity in the presence of nitrate, while glutamine synthetase activity remained unaltered.http://link.springer-ny. com/link/service/journals/00284/bibs/39n5p237.html</HEA
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PMID:Mutants of the cyanobacterium anabaena sp. PCC 7120 altered in nitrate transport and reduction 1048 30

Exposure of cells of cyanobacteria (blue-green algae) grown under high-CO(2) conditions to inorganic C-limitation induces transcription of particular genes and expression of high-affinity CO(2) and HCO(3)(-) transport systems. Among the low-CO(2)-inducible transcription units of Synechococcus sp. strain PCC 7942 is the cmpABCD operon, encoding an ATP-binding cassette transporter similar to the nitrate/nitrite transporter of the same cyanobacterium. A nitrogen-regulated promoter was used to selectively induce expression of the cmpABCD genes by growth of transgenic cells on nitrate under high CO(2) conditions. Measurements of the initial rate of HCO(3)(-) uptake after onset of light, and of the steady-state rate of HCO(3)(-) uptake in the light, showed that the controlled induction of the cmp genes resulted in selective expression of high-affinity HCO(3)(-) transport activity. The forced expression of cmpABCD did not significantly increase the CO(2) uptake capabilities of the cells. These findings demonstrated that the cmpABCD genes encode a high-affinity HCO(3)(-) transporter. A deletion mutant of cmpAB (M42) retained low CO(2)-inducible activity of HCO(3)(-) transport, indicating the occurrence of HCO(3)(-) transporter(s) distinct from the one encoded by cmpABCD. HCO(3)(-) uptake by low-CO(2)-induced M42 cells showed lower affinity for external HCO(3)(-) than for wild-type cells under the same conditions, showing that the HCO(3)(-) transporter encoded by cmpABCD has the highest affinity for HCO(3)(-) among the HCO(3)(-) transporters present in the cyanobacterium. This appears to be the first unambiguous identification and description of a primary active HCO(3)(-) transporter.
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PMID:Identification of an ATP-binding cassette transporter involved in bicarbonate uptake in the cyanobacterium Synechococcus sp. strain PCC 7942. 1055 62

The nrtP and narB genes, encoding nitrate/nitrite permease and nitrate reductase, respectively, were isolated from the marine cyanobacterium Synechococcus sp. strain PCC 7002 and characterized. NrtP is a member of the major facilitator superfamily and is unrelated to the ATP-binding cassette-type nitrate transporters that previously have been described for freshwater strains of cyanobacteria. However, NrtP is similar to the NRT2-type nitrate transporters found in diverse organisms. An nrtP mutant strain consumes nitrate at a 4.5-fold-lower rate than the wild type, and this mutant grew exponentially on a medium containing 12 mM nitrate at a rate approximately 2-fold lower than that of the wild type. The nrtP mutant cells could not consume nitrite as rapidly as the wild type at pH 10, suggesting that NrtP also functions in nitrite uptake. A narB mutant was unable to grow on a medium containing nitrate as a nitrogen source, although this mutant could grow on media containing urea or nitrite with rates similar to those of the wild type. Exogenously added nitrite enhanced the in vivo activity of nitrite reductase in the narB mutant; this suggests that nitrite acts as a positive effector of nitrite reductase. Transcripts of the nrtP and narB genes were detected in cells grown on nitrate but were not detected in cells grown on urea or ammonia. Transcription of the nrtP and narB genes is probably controlled by the NtcA transcription factor for global nitrogen control. The discovery of a nitrate/nitrite permease in Synechococcus sp. strain PCC 7002 suggests that significant differences in nutrient transporters may occur in marine and freshwater cyanobacteria.
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PMID:A novel nitrate/nitrite permease in the marine Cyanobacterium synechococcus sp. strain PCC 7002. 1057 42

In Synechocystis PCC 6803 as in other cyanobacteria, involvement of protein PII in the co-regulation of inorganic carbon and nitrogen metabolism was established based on post-translational modifications of the protein resulting from changes in the carbon/nitrogen regimes. Uptake of bicarbonate and nitrate in response to changes of the carbon and/or nitrogen regimes is altered in a PII-null mutant, indicating that both processes are under control of PII. Modulation of electron flow by addition of methyl viologen with or without duroquinol, or in a NAD(P)H dehydrogenase-deficient mutant, affects the phosphorylation level of PII. The redox state of the cells would thus act as a trigger for PII phosphorylation.
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PMID:Protein PII regulates both inorganic carbon and nitrate uptake and is modified by a redox signal in synechocystis PCC 6803. 1060 24

The feasibility of biologically removing nitrate from groundwater was tested by using cyanobacterial cultures in batch mode under laboratory conditions. Results demonstrated that nitrate-contaminated groundwater, when supplemented with phosphate and some trace elements, can be used as growth medium supporting vigorous growth of several strains of cyanobacteria. As cyanobacteria grew, nitrate was removed from the water. Of three species tested, Synechococcus sp. strain PCC 7942 displayed the highest nitrate uptake rate, but all species showed rapid removal of nitrate from groundwater. The nitrate uptake rate increased proportionally with increasing light intensity up to 100 micromol of photons m(-2) s(-1), which parallels photosynthetic activity. The nitrate uptake rate was affected by inoculum size (i.e., cell density), fixed-nitrogen level in the cells in the inoculum, and aeration rate, with vigorously aerated, nitrate-sufficient cells in mid-logarithmic phase having the highest long-term nitrate uptake rate. Average nitrate uptake rates up to 0.05 mM NO(3-) h(-1) could be achieved at a culture optical density at 730 nm of 0.5 to 1. 0 over a 2-day culture period. This result compares favorably with those reported for nitrate removal by other cyanobacteria and algae, and therefore effective nitrate removal from groundwater using this organism could be anticipated on large-scale operations.
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PMID:Removal of nitrate from groundwater by cyanobacteria: quantitative assessment of factors influencing nitrate uptake. 1061 14

The narC locus required for assimilatory nitrate reduction in the cyanobacterium Synechococcus sp. strain PCC 7942 was found to carry a mobA gene for molybdopterin guanine dinucleotide biosynthesis. Insertional inactivation of this gene blocked production of nitrate reductase in Synechococcus cells. We have previously described Synechococcus genes encoding homologues to molybdopterin biosynthesis proteins including MoaA, MoaC/MoaB, MoaD, MoaE, and MoeA, but not to MoeB. A cyanobacterial gene putatively encoding a protein composed of an amino-terminal domain of 260 amino acids homologous to Escherichia coli MoeB and of a carboxy-terminal extension of 130 amino acids was identified. Synechococcus mutants bearing only inactive versions of this putative moeB gene could not be isolated suggesting that it has function(s) additional to molybdopterin biosynthesis.
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PMID:Molybdopterin guanine dinucleotide cofactor in Synechococcus sp. nitrate reductase: identification of mobA and isolation of a putative moeB gene. 1062 25

In the cyanobacterium Synechococcus sp. strain PCC 7942, the phosphorylation states of the signal transducer PII protein (GlnB) can change rapidly depending on the nitrogen and carbon supply. A PII-null mutant (MP2) shows no ammonium-dependent inhibition of the nitrate and nitrite uptake, in contrast to the wild-type. New mutants with different types of PII, which may mimic either the phosphorylated (GlnBS49E or GlnBS49D) or unphosphorylated (GlnBS49A) form of the protein, were constructed using site-directed in vitro mutagenesis. Mutant MP2-A (GlnBS49A) grew poorly using nitrate as a nitrogen source and was unable to take up nitrate supplied at 100 microM, even in the absence of externally added ammonium. Mutants MP2-D and MP2-E (GlnBS49D and GlnBS49E, respectively), however, showed nitrate-dependent growth and regulation of nitrate uptake by ammonium, as in the wild-type. Characterization of the mutants also included an analysis of nitrite uptake and of the levels of the nir (nitrate/nitrite assimilation) operon transcripts, the presence of NrtA (nitrate/nitrite transport binding protein), and nitrate and nitrite reductase activities. In vitro, no significant difference was observed in the cooperative binding of ATP and 2-oxoglutarate between the wild-type and the unphosphorylated or phosphorylated-like forms of the mutant PII proteins. The results obtained indicate that both unphosphorylated and phosphorylated-like forms of PII are able to inhibit nitrate uptake in the presence of ammonium, but the unphosphorylated form also has a negative effect in the absence of this nitrogen source. Therefore, an additional effector, possibly 2-oxoglutarate, is required for the PII protein to relieve inhibition of nitrate uptake in the absence of ammonium.
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PMID:Phosphorylation of the signal transducer PII protein and an additional effector are required for the PII-mediated regulation of nitrate and nitrite uptake in the Cyanobacterium synechococcus sp. PCC 7942. 1063 30

The presence of NaCl in the nutrient solution promoted nitrate uptake in parent Anabaena sp. PCC 7120, mutants SP7 (defective in nitrate reductase activity) and SP17 (partially defective in nitrate reductase activity), but not in the mutant SP9 (defective in nitrate transport and reduction). Nitrate reductase activity of the parent and mutant SP17 increased with increasing concentration of nitrate in saline medium, while mutants SP7 and SP9 did not respond to the altered salinity. Although Na+ was not required for nitrate reductase activity, its presence in the nutrient solution enhanced nitrate reduction. Complete removal of Na+ from the nutrient solution markedly reduced nitrogenase activity in all the strains, while raising the concentration of NaCl to 50 mmol l-1 or above, was equally toxic to nitrogenase activity. External NaCl at 200 mmol l-1 brought down the nitrogenase activity to the same residual level as observed without Na+.
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PMID:Response to NaCl of nitrate assimilation and nitrogenase activity of the cyanobacterium Anabaena sp. PCC 7120 and its mutants. 1069 73

The cmpABCD operon of the cyanobacterium Synechococcus sp. strain PCC 7942 encodes an ATP-binding cassette transporter involved in HCO(3)(-) uptake. The three genes, cmpBCD, encode membrane components of an ATP-binding cassette transporter, whereas cmpA encodes a 42-kDa cytoplasmic membrane protein, which is 46.5% identical to the membrane-anchored substrate-binding protein of the nitrate/nitrite transporter. Equilibrium dialysis analysis using H(14)CO(3)(-) showed that a truncated CmpA protein lacking the N-terminal 31 amino acids, expressed in Escherichia coli cells as a histidine-tagged soluble protein, specifically binds inorganic carbon (CO(2) or HCO(3)(-)). The addition of the recombinant CmpA protein to a buffer caused a decrease in the concentration of dissolved CO(2) because of the binding of inorganic carbon to the protein. The decrease in CO(2) concentration was accelerated by the addition of carbonic anhydrase, indicating that HCO(3)(-), but not CO(2), binds to the protein. Mass spectrometric measurements of the amounts of unbound and bound HCO(3)(-) in CmpA solutions containing low concentrations of inorganic carbon revealed that CmpA binds HCO(3)(-) with high affinity (K(d) = 5 microm). A similar dissociation constant was obtained by analysis of the competitive inhibition of the CmpA protein on the carboxylation of phosphoenolpyruvate by phosphoenolpyruvate carboxylase at limiting concentrations of HCO(3)(-). These findings showed that the cmpA gene encodes the substrate-binding protein of the HCO(3)(-) transporter.
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PMID:Bicarbonate binding activity of the CmpA protein of the cyanobacterium Synechococcus sp. strain PCC 7942 involved in active transport of bicarbonate. 1077 19

Mutants of Anabaena sp. PCC 7120 resistant to chlorate were isolated using transposon mutagenesis. The Anabaena population of 5 x 10(7) cells ml(-1) and log phase Escherichia coli cultures in undisturbed conditions produced maximum exconjugants. Nitrate-promoted growth and cellular constituents observed in the parent were absent in the mutants. Nitrate repressed heterocyst formation and N2-fixation in the parent, but had little or no effect on the mutants.
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PMID:Isolation and characterization of transposon-induced chlorate resistant mutants of the cyanobacterium Anabaena species PCC 7120. 1088


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