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1.
Response to NaCl of nitrate assimilation and nitrogenase activity of the cyanobacterium Anabaena sp. PCC 7120 and its mutants 总被引:1,自引:1,他引:0
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+. 相似文献
2.
Comamonas testosteroni P15 and its mutant strain E23 can tolerate and utilize phenol as the sole source of carbon and energy at up to 15 mM and
20 mM, respectively. Compared to the wild type P15, mutant E23 showed higher values of K
s and K
i but a lower μmax value, and had lower phenol hydroxylase and catechol 2,3-dioxygenase activities. Without phenol exposure, mutant E23 demonstrated
a two-fold greater amount of cardiolipin than the wild type P15. Upon exposure to phenol, an increase in cardiolipin at the
expense of phosphatidylethanolamine was observed in the wild type P15. However, there was no significant difference in major
phospholipid contents between mutant E23 cells grown in the presence or absence of phenol. It was noted that the ratio of
trans/cis fatty acids of phosphatidylethanolamine and cardiolipin in mutant E23 was 65–70% higher than that in the wild type P15. In
the absence of phenol, the degree of saturation of cardiolipin in mutant E23 was 33% higher than that in wild type P15. In
contrast to earlier findings, an increase in C16:1 9trans with a simultaneous decrease in C18:1 11cis instead of C16:1 9cis
was observed in specific classes of phospholipids.
Received: 30 July 1998 / Received last revision: 16 November 1998 / Accepted: 12 December 1998 相似文献
3.
Ruth M. Siewe Brita Weil Andreas Burkovski Lothar Eggeling R. Krämer Thomas Jahns 《Archives of microbiology》1998,169(5):411-416
When Corynebacterium glutamicum is grown with a sufficient nitrogen supply, urea crosses the cytoplasmic membrane by passive diffusion. A permeability coefficient
for urea diffusion of 9 × 10–7 cm s–1 was determined. Under conditions of nitrogen starvation, an energy-dependent urea uptake system was synthesized. Carrier-mediated
urea transport was catalyzed by a secondary transport system linked with proton motive force. With a K
m for urea of 9 μM, the affinity of this uptake system was much higher than the affinity of urease towards its substrate (K
m approximately 55 mM urea). The maximum uptake velocity depended on the expression level and was relatively low [2–3.5 nmol
min–1 (mg dry wt.)–1].
Received: 11 August 1997 / Accepted: 2 December 1997 相似文献
4.
The pericarp of the dormant sugarbeet fruit acts as a storage reservoir for nitrate, ammonium and -amino-N. These N-reserves enable an autonomous development of the seedling for 8–10 d after imbibition. The nitrate content of the seed (1% of the whole fruit) probably induces nitrate-reductase activity in the embryo enclosed in the pericarp. Nitrate that leaks out of the pericarp is reabsorbed by the emerging radicle. Seedlings germinated from seeds (pericarp was removed) without external N-supply are able to take up nitrate immediately upon exposure via a low-capacity uptake system (vmax = 0.8 mol NO
3
-
·(g root FW)–1·h–1; Ks = 0.12 mM). We assume that this uptake system is induced by the seed nitrate (10 nmol/seed) during germination. Induction of a high-capacity nitrate-uptake system (vmax = 3.4 mol NO
3
-
·(g root FW)–1·h–1; Ks = 0.08 mM) by externally supplied nitrate occurs after a 20-min lag and requires protein synthesis. Seedlings germinated from whole fruits absorb nitrate via a highcapacity uptake mechanism induced by the pericarp nitrate (748 nmol/pericarp) during germination. The uptake rates of the high-capacity system depend only on the actual nitrate concentration of the uptake medium and not on prior nitrate pretreatments. Nitrate deprivation results in a decline of the nitrate-uptake capacity (t1/2 of vmax = 5 d) probably caused by the decay of carrier molecules. Small differences in Ks but significant differences in vmax indicate that the low- and high-capacity nitrate-uptake systems differ only in the number of identical carrier molecules.Abbreviations NR
nitrate reductase
-
pFPA
para-fluorophenylalanine
This work was supported by a grant from Bundesministerium für Forschung und Technologie and by Kleinwanzlebener Saatzucht AG, Einbeck. 相似文献
5.
Baebprasert Wipawee Karnchanatat Aphichart Lindblad Peter Incharoensakdi Aran 《World journal of microbiology & biotechnology》2011,27(10):2467-2473
In the non-diazotrophic cyanobacterium Synechocystis sp. strain PCC 6803, an osmolality of 30 and 40 mosmol/kg sorbitol and NaCl resulted in 3.5- and 4.5-fold increase of nitrate
uptake, respectively. The NaCl-stimulated uptake was abolished by treatment with chloramphenicol. At 25 mosmol/kg or higher,
NaCl induced higher nitrate uptake than sorbitol suggesting an ionic effect of Na+. The nitrate uptake in Synechocystis showed K
s
and V
max values of 46 μM and 1.37 μmol/min/mg Chl, respectively. Mutants disrupted in nitrate and nitrite reductase exhibited a decreased
nitrate uptake. Ammonium, chlorate, and dl-glyceraldehyde caused a reduction of nitrate uptake. Dark treatment caused a drastic reduction of uptake by 70% suggesting
an energy-dependent system. Nitrate transport was sensitive to various metabolic inhibitors including those dissipating proton
gradients and membrane potential. The results suggest that nitrate uptake in Synechocystis is stimulated by Na+ ions and requires energy provided by the functioning electron transport chain. 相似文献
6.
Francisco Martínez Murillo Theresa Gugliuzza John Senko Partha Basu J. F. Stolz 《Archives of microbiology》1999,172(5):313-320
Nitrate reduction in the dissimilatory iron-reducing bacterium Geobacter metallireducens was investigated. Nitrate reductase and nitrite reductase activities in nitrate-grown cells were detected only in the membrane
fraction. The apparent K
m values for nitrate and nitrite were determined to be 32 and 10 μM, respectively. Growth on nitrate was not inhibited by either
tungstate or molybdate at concentrations of 1 mM or less, but was inhibited by both at 10 and 20 mM. Nitrate and nitrite reductase
activity in the membrane fraction was not, however, affected by dialysis with 20 mM tungstate. An enzyme complex that exhibited
both nitrate and nitrite reductase activity was solubilized from membrane fractions with CHAPS and was partially purified
by preparative gel electrophoresis. It was found to be composed of four different polypeptides with molecular masses of 62,
52, 36, and 16 kDa. The 62-kDa polypeptide [a low-midpoint potential (–207 mV), multiheme cytochrome c] exhibited nitrite reductase activity under denaturing conditions. No molybdenum was detected in the complex by plasma-emission
mass spectrometry.
Received: 26 March 1999 / Accepted: 16 August 1999 相似文献
7.
Merja R. Häkkinen Mervi T. Hyvönen Seppo Auriola Robert A. Casero Jr Jouko Vepsäläinen Alex R. Khomutov Leena Alhonen Tuomo A. Keinänen 《Amino acids》2010,38(2):369-381
N-alkylated polyamine analogues have potential as anticancer and antiparasitic drugs. However, their metabolism in the host
has remained incompletely defined thus potentially limiting their utility. Here, we have studied the degradation of three
different spermine analogues N,N′-bis-(3-ethylaminopropyl)butane-1,4-diamine (DESPM), N-(3-benzyl-aminopropyl)-N′-(3-ethylaminopropyl)butane-1,4-diamine (BnEtSPM) and N,N′-bis-(3-benzylaminopropyl)butane-1,4-diamine (DBSPM) and related mono-alkylated derivatives as substrates of recombinant
human polyamine oxidase (APAO) and spermine oxidase (SMO). APAO and SMO metabolized DESPM to EtSPD [K
m(APAO) = 10 μM, k
cat(APAO) = 1.1 s−1 and K
m(SMO) = 28 μM, k
cat(SMO) = 0.8 s−1, respectively], metabolized BnEtSPM to EtSPD [K
m(APAO) = 0.9 μM, k
cat(APAO) = 1.1 s−1 and K
m(SMO) = 51 μM, k
cat(SMO) = 0.4 s−1, respectively], and metabolized DBSPM to BnSPD [K
m(APAO) = 5.4 μM, k
cat(APAO) = 2.0 s−1 and K
m(SMO) = 33 μM, k
cat(SMO) = 0.3 s−1, respectively]. Interestingly, mono-alkylated spermine derivatives were metabolized by APAO and SMO to SPD [EtSPM K
m(APAO) = 16 μM, k
cat(APAO) = 1.5 s−1; K
m(SMO) = 25 μM, k
cat(SMO) = 8.2 s−1; BnSPM K
m(APAO) = 6.0 μM, k
cat(APAO) = 2.8 s−1; K
m(SMO) = 19 μM, k
cat(SMO) = 0.8 s−1, respectively]. Surprisingly, EtSPD [K
m(APAO) = 37 μM, k
cat(APAO) = 0.1 s−1; K
m(SMO) = 48 μM, k
cat(SMO) = 0.05 s−1] and BnSPD [K
m(APAO) = 2.5 μM, k
cat(APAO) = 3.5 s−1; K
m(SMO) = 60 μM, k
cat(SMO) = 0.54 s−1] were metabolized to SPD by both the oxidases. Furthermore, we studied the degradation of DESPM, BnEtSPM or DBSPM in the
DU145 prostate carcinoma cell line. The same major metabolites EtSPD and/or BnSPD were detected both in the culture medium
and intracellularly after 48 h of culture. Moreover, EtSPM and BnSPM were detected from cell samples. Present data shows that
inducible SMO parallel with APAO could play an important role in polyamine based drug action, i.e. degradation of parent drug
and its metabolites, having significant impact on efficiency of these drugs, and hence for the development of novel N-alkylated polyamine analogues. 相似文献
8.
Patricia Melin Caroline Norez Isabelle Callebaut Frédéric Becq 《The Journal of membrane biology》2006,208(3):203-212
The cystic fibrosis transmembrane conductance regulator (CFTR) protein contains a canonical ATP-binding cassette (ABC) signature
motif, LSGGQ, in nucleotide binding domain 1 (NBD1) and a degenerate LSHGH in NBD2. Here, we studied the contribution of the conserved residues G551 and G1349 to the pharmacological modulation of
CFTR chloride channels by phloxine B using iodide efflux and whole-cell patch clamp experiments performed on the following
green fluorescent protein (GFP)-tagged CFTR: wild-type, delF508, G551D, G1349D, and G551D/G1349D double mutant. We found that
phloxine B stimulates and inhibits channel activity of wild-type CFTR (Ks = 3.2 ± 1.6 μM, Ki = 38 ± 1.4 μM) and delF508 CFTR (Ks = 3 ± 1.8 μM, Ki = 33 ± 1 μM). However, CFTR channels with the LSGDQ mutated motif (mutation G551D) are activated (Ks = 2 ± 1.13 μM) but not inhibited by phloxine B. Conversely, CFTR channels with the LSHDH mutated motif (mutation G1349D) are inhibited (Ki = 40 ± 1.01 μM) but not activated by phloxine B. Finally, the double mutant G551D/G1349D CFTR failed to respond not only to phloxine B stimulation
but also to phloxine B inhibition, confirming the importance of both amino acid locations. Similar results were obtained with
genistein, and kinetic parameters were determined to compare the pharmacological effects of both agents. These data show that
G551 and G1349 control the inhibition and activation of CFTR by these agents, suggesting functional nonequivalence of the
signature motifs of NBD in the ABC transporter CFTR. 相似文献
9.
Balakumar T. Selvakumar V. Sathiameena K. Ilanchezhian C. Murugu Paliwal K. 《Photosynthetica》1999,37(3):459-467
The kinetics and other characteristics of nitrate reductase (NR, EC 1.6.6.1) in cowpea [Vigna unguiculata (L.) Walp.] seedlings irradiated with biologically effective UV-B radiation (280-320 nm, 3.2 W m-2 s-1) were recorded. The in vivo and in vitro NR activities were inhibited by 34 and 41 % under UV-B treatment, respectively. Both Vmax and Km for the substrate were enhanced by UV-B radiation. The Km for nitrate increased from 1.2 to 1.7 mM after the UV-B irradiation. The change in Km for NADH was from 0.12 to 0.17 mM. The increases in Km indicate that UV-B radiation seriously changes the topology of NR, particularly with respect to the nitrate and NADH binding
sites. The rate of NR turnover indicates the extent of damage inflicted by UV-B radiation on the nitrate metabolism. The half-life
(t1/2) of NR was reduced from 7 to 4 h in the UV-B treated seedlings. UV-B also inhibited the kinetics of nitrate uptake by plants:
its Km increased from 0.08 to 0.12 mM.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
10.
UDP-glucose dehydrogenase (UDPGDH) activity was detected in extracts of maize cell-cultures and developing leaves. The reaction product was confirmed as UDP-glucuronate. Leaf extracts from null mutants defective in one or both of the ethanol dehydrogenase genes, ADH1 and ADH2, had similar UDPGDH activities to wild-type, showing that UDPGDH activity is not primarily due to ADH proteins. The mutants showed no defect in their wall matrix pentose:galactose ratios, or matrix:cellulose ratio, showing that ADHs were not required for normal wall biosynthesis. The majority of maize leaf UDPGDH activity had K
m (for UDP-glucose) 0.5–1.0 mM; there was also a minor activity with an unusually high K
m of >50 mM. In extracts of cultured cells, kinetic data indicated at least three UDPGDHs, with K
m values (for UDP-glucose) of roughly 0.027, 2.8 and >50 mM (designated enzymes EL, EM and EH respectively). EM was the single major contributor to extractable UDPGDH activity when assayed at 0.6–9.0 mM UDP-Glc. Most studies, in other plant species, had reported only EL-like isoforms. Ethanol (100 mM) partially inhibited UDPGDH activity assayed at low, but not high, UDP-glucose concentrations, supporting the conclusion that at least EH activity is not due to ADH. At 30 μM UDP-glucose, 20–150 μM UDP-xylose inhibited UDPGDH activity, whereas 5–15 μM UDP-xylose promoted it. In conclusion, several very different UDPGDH isoenzymes contribute to UDP-glucuronate and hence wall matrix biosynthesis in maize, but ADHs are not responsible for these activities. 相似文献
11.
Loss of function of the Wfs1 gene causes Wolfram syndrome, a rare multisystem degenerative disorder. Mutant mice with targeted
Wfs1 gene disruption (Wfs1 KO) display morphological and behavioral impairments that are not well understood. The present
study aimed to investigate the striatal dopamine output of wild-type, heterozygous, and homozygous Wfs1 null-mutant mice using
in vivo microdialysis technique. The baseline dopamine output in striatum was similar in all three animal groups. The application
of 100 mM [K+]-rich modified Ringer solution caused in homozygous Wfs1 mutant mice an increase of dopamine output by 400%, while in wild-type
and heterozygous animals, the increase of the dopamine output yielded up to 1,200%. In sum, the homozygous Wfs1 mutant mice
(AUC0–3 = 0.212 nM/μl h) show significantly decreased striatal dopamine output in response to high-concentration [K+] challenge as compared with wild-type or heterozygous Wfs1 mutant conspecifics (AUC0–3 = 0.427 and 0.505 nM/μl h, respectively). This could explain at least some of the behavioral alterations in Wfs1 mutant mice. 相似文献
12.
Elevation of the external potassium concentration induced a two-phase inward current in freshly isolated pyramidal hippocampal
neurons. This current was voltage-dependent and demonstrated strong inward rectification. The current consisted of a leakage
current and a time-dependent current (τ=40–50 msec at 21°C); the latter was designated asI
ΔK. As was shown earlier, K+ is a major charge carrier in the development of slow potassium-activated current. The pharmacological properties ofI
ΔK were studied using a patch-clamp technique.I
ΔK was completely blocked by external 10 mM TEA or 5 mM Ba2+ (IC50=480±90mM) and exhibited low sensitivity to extracellular Cs+ (2 mM). This current was not affected by 1 mM 4-aminopyridine and was insensitive to a muscarinic agonist, carbachol (50
μM), and to 1 mM extracellular Cd2+. Elevation of external Ca2+ from 2.5 mM to 10 mM did not changeI
ΔK. Our data indicate that the pharmacological properties ofI
ΔK differ from those of other voltage-gated potassium currents, but more specific blockers must be used to make this evidence
conclusive. 相似文献
13.
Xuejun Hu Sylvain Robin Shane O’Connell Gary Walsh J. Gerard Wall 《Applied microbiology and biotechnology》2010,87(5):1773-1782
β-galactosidase is an enzyme administered as a digestive supplement to treat lactose intolerance, a genetic condition prevalent
in most world regions. The gene encoding an acid-stable β-galactosidase potentially suited for use as a digestive supplement
was cloned from Aspergillus niger van Tiegh, sequenced and expressed in Pichia pastoris. The purified recombinant protein exhibited kinetic properties similar to those of the native enzyme and thus was also competitively
inhibited by its product, galactose, at application-relevant concentrations. In order to alleviate this product inhibition,
a model of the enzyme structure was generated based on a Penicillium sp. β-galactosidase crystal structure with bound β-galactose. This led to targeted mutagenesis of an Asp258-Ser-Tyr-Pro-Leu-Gly-Phe amino acid motif in the A. niger van Tiegh enzyme and isolation from the resultant library of a mutant β-galactosidase enzyme with reduced sensitivity to
inhibition by galactose (K
i of 6.46 mM galactose, compared with 0.76 mM for the wildtype recombinant enzyme). The mutated enzyme also exhibited an increased
K
m (3.76 mM compared to 2.21 mM) and reduced V
max (110.8 μmol min−1 mg−1 compared to 172.6 μmol min−1 mg−1) relative to the wild-type enzyme, however, and its stability under simulated fasting gastric conditions was significantly
reduced. The study nevertheless demonstrates the potential to rationally engineer the A. niger van Tiegh enzyme to relieve product inhibition and create mutants with improved, application-relevant kinetic properties
for treatment of lactose intolerance. 相似文献
14.
The DR2356 nudix hydrolase gene from Deinococcus radiodurans has been cloned and the product expressed as an 18 kDa histidine-tagged protein. The enzyme hydrolysed adenosine and diadenosine polyphosphates, always generating ATP as one of the initial products. ATP and other (deoxy)nucleoside triphosphates were also substrates, yielding (d)NDP and Pi as products. The DR2356 protein was most active at pH 8.6–9.0 and showed a strong preference for Mn2+ as activating cation. Mg2+ ions at 15 mM supported only 5% of the activity achieved with 2 mM Mn2+. K
m and k
cat values for diadenosine tetra-, penta- and hexaphosphates were 2.0, 2.4 and 1.1 μM and 11.4, 28.6 and 12.0 s−1, respectively, while for GTP they were 20.3 μM and 1.8 s−1, respectively. The K
m for adenosine 5′-pentaphosphate was <1 μM. Expression analysis showed the DR2356 gene to be induced eight- to ninefold in stationary phase and in cells subjected to slow dehydration plus rehydration. Superoxide (but not peroxide) treatment and rapid dehydration caused a two-to threefold induction. The Mn-requirement and induction in stationary phase suggest that DR2356 may have a specific role in maintenance mode metabolism in stationary phase as Mn2+ accumulates. 相似文献
15.
E. Jacobsen 《Plant and Soil》1984,82(3):427-438
Summary In pea (Pisum sativum L.), mutants could be induced, modified in the symbiotic interaction withRhizobium leguminosarum. Among 250 M2-families, two nodulation resistant mutants (K5 and K9) were obtained. In mutant K5 the nodulation resistance was monogenic recessive and not Rhizobium strain specific. Out of 220 M2-families one mutant nod3 was found which could form nodules at high nitrate concentrations (15 mM KNO3). This mutant nodulated abundantly with severalRhizobium strains, both in the absence and presence of nitrate. Probably as the result of a pleiotropic effect, its root morphology was also changed. Among 1800 M2-families, five nitrate reductase deficient mutants were obtained and one of them (mutant E1) was used to study the inhibitory effect of nitrate on nodulation and nitrogen fixation.The results of the present investigation show that pea mutants which are modified in their symbiosis withRhizobium leguminosarum, can readily be obtained. The significance of such mutants for fundamental studies of the legume-Rhizobium symbiosis and for applications in plant breeding is discussed. 相似文献
16.
Christopher D. Skory 《Current microbiology》2003,46(1):0059-0064
A thalium chloride-resistant (TlClr) mutant strain and a sodium chloride-resistant (NaClr) mutant strain of the diazotrophic cyanobacterium Anabaena variabilis have been isolated by spontaneous and chemical mutagenesis by using TlCl, a potassium (K+) analog, and nitrosoguanidine (NTG), respectively. The TlClr mutant strain was found to be defective in K+ transport and showed resistance against 10 μM TlCl. However, it also showed sensitivity against NaCl (LD50, 50 mM). In contrast, neither wild-type A. variabilis nor its NaClr mutant strain could survive in the presence of 10 μM TlCl and died even at 1 μM TlCl. The TlClr mutant strain exhibited almost negligible K+ uptake, indicating the lack of a K+ uptake system. High K+ uptake was, however, observed in the NaClr mutant strain, reflecting the presence of an active K+ uptake system in this strain.
DCMU, an inhibitor of PS II, inhibited the K+ uptake in wild-type A. variabilis and its TlClr and NaClr mutant strains, suggesting that K+ uptake in these strains is an energy-dependent process and that energy is derived from photophosphorylation. This contention
is further supported by the inhibition of K+ uptake under dark conditions. Furthermore, the inhibition of K+ uptake by KCN, DNP, and NaN3 also suggests the involvement of oxidative phosphorylation in the regulation of an active K+ uptake system.
The whole-cell protein profile of wild-type A. variabilis and its TlClr and NaClr mutant strains growing in the presence of 50 mM KCl was made in the presence and absence of NaCl. Lack of transporter proteins in TlClr mutant strain suggests that these proteins are essentially required for the active transport and accumulation of K+ and make this strain NaCl sensitive. In contrast, strong expression of the transporter proteins in NaClr mutant strain and its weak expression in wild-type A. variabilis is responsible for their resistance and sensitivity to NaCl, respectively. Therefore, it appears that the increased salt
tolerance of the NaClr mutant strain was owing to increased K+ uptake and accumulation, whereas the salt sensitivity of the TlClr mutant strain was owing to the lack of K+ uptake and accumulation.
Received: 7 March 2002 / Accepted: 8 April 2002 相似文献
17.
S. Quratulain B. Nasira M.A. Kashmiri 《World journal of microbiology & biotechnology》2006,22(3):213-218
Summary The penicillin G amidase (PGA) activity of a parent strain of E. coli (PCSIR-102) was enhanced by chemical mutagenization with N-methyl-N′-nitro-N-nitrosoguanidine (MNNG). After screening and optimization, a penicillinase deficient mutant (MNNG-37) was isolated and found
effective for the production of penicillin G amidase as compared to the parent strain of E. coli (PCSIR-102). Penicillin G amidase activity of MNNG-37 appeared during an early stage of growth, whereas PCSIR-102 did not
exhibit PGA activity due to the presence of penicillinase enzyme which inhibits the activity of enzyme PGA. However, MNNG-37
gave a three-fold increase in enzyme activity (231 IU mg−1) as compared to PCSIR-102 (77 IU mg−1) in medium containing 0.15 and 0.1% concentrations of phenylacetic acid, respectively which was added after 6 h of cultivation.
The difference in K
m values of the enzyme produced by parent strain PCSIR-102 (0.26 mM) and mutant strain MNNG-37 (0.20 mM) is significant (1.3-fold
increase in K
m value) which may show the superiority of the latter in terms of better enzyme properties. 相似文献
18.
The production of biomass, polysaccharide storage material and H2 from malate was studied in the wild-type and mutants RdcI, RdcII and RdcI/cII of Rhodobacter capsulatus. The mutants are defective in either copy I, copy II or both copies of the nitrogenase genes nifA and nifB. Stationary phase levels of biomass, polysaccharide and H2 were determined in phototrophic batch cultures grown with 30 mM of d,l-malate and either 2, 5, or 8 mM of ammonium or 7 mM of glutamate. Calculation of the amounts of malate converted into the
three products revealed that, at 8 mM of ammonium and 7 mM of glutamate, malate consumption and product formation were balanced.
But with decreasing ammonium concentrations malate not converted into biomass was utilized with decreasing efficiency in polysaccharide
and H2 formation. This suggests formation of unknown products at the lower ammonium concentrations. Under conditions of optimal
N supply, 80% of the malate not used for biomass production was converted by the wild-type and strain RdcII to H2 and CO2. Mutant RdcI exhibited slightly decreased H2 production. The double mutant did not evolve H2 but accumulated increased amounts of polysaccharide. However, the amounts of polysaccharide were lower than should be expected
if all of the spare malate, not utilized by the double mutant for H2 production, was converted into storage material. This and incomplete conversion of malate into known products at low ammonium
supplies suggests that polysaccharide accumulation does not compete with the process of H2 formation for malate. 相似文献
19.
Irena Romanowska Ewa Kwapisz Magdalena Mitka Stanisław Bielecki 《Journal of industrial microbiology & biotechnology》2010,37(6):625-629
Gordonia alkanivorans S7 is an efficient degrader of fuel oil hydrocarbons that can simultaneously utilize oxygen and nitrate as electron acceptors.
The respiratory nitrate reductase (Nar) from this organism has been isolated using ion exchange chromatography and gel filtration,
and then preliminarily characterized. PAGE, SDS-PAGE and gel filtration chromatography revealed that Nar consisted of three
subunits of 103, 53 and 25 kDa. The enzyme was optimally active at pH 7.9 and 40°C. K
m values for NO3
− (110 μM) and for ClO3
− (138 μM) were determined for a reduced viologen as an electron donor. The purified Nar did not use NADH as the electron donor
to reduce nitrate or chlorate. Azide was a strong inhibitor of its activity. Our results imply that enzyme isolated from G. alkanivorans S7 is a respiratory membrane-bound nitrate reductase. This is the first report of purification of a nitrate reductase from
Gordonia species. 相似文献
20.
A mixed culture of microorganisms able to utilize 4,6-dinitro-ortho-cresol (DNOC) as the sole source of carbon, nitrogen and energy was isolated from soil contaminated with pesticides and from
activated sludge. DNOC was decomposed aerobically in batch cultures as well as in fixed-bed column reactors. Between 65% and
84% of the substrate nitrogen was released as nitrate into the medium, and 61% of the carbon from uniformly 14C-labelled DNOC was recovered as 14CO2. The mixed microbial culture also decomposed 4-nitrophenol and 2,4-dinitrophenol but not 2,3-dinitrophenol, 2,6-dinitrophenol,
2,4-dinitrotoluene, 2,4-dinitrobenzoic acid or 2-sec-butyl-4,6-dinitrophenol (Dinoseb). Maximal degradation rates for DNOC by the bacterial biofilm immobilized on glass beads
in fixed-bed column reactors were 30 mmol day−1 (l reactor volume)−1, leaving an effluent concentration of less than 5 μg l−1 DNOC in the outflowing medium. The apparent K
s value of the immobilized mixed culture for DNOC was 17 μM. Degradation was inhibited at DNOC concentrations above 30 μM and
it ceased at 340 μM, possibly because of the uncoupling action of the nitroaromatic compound on the cellular energy-transducing
mechanism.
Received: 27 March 1997 / Received revision: 5 June 1997 / Accepted: 7 June 1997 相似文献