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1.
Radish (Raphanus sativus L.) seedlings pretreated with different hormones viz. kinetin, gibberellic acid and abscisic acid were subjected to different
N-forms. The seedlings were treated with different concentrations of KNO3, NH4Cl and NH4NO3 and the changes in nitrate reductase activity were seen in light and dark conditions in the cotyledons. Nitrate reductase
activity was affected differently by hormone application. Nitrate increased and ammonia decreased nitrate reductase activity;
in both light and dark-grown seedlings KNO3 induced more in vitro nitrate reductase activity. NH
4
+
when combined with NO
3
−
, however, could level up to some extent, with KNO3 in light, except in kinetin. A transient response of induction of NR activity was evident with decreased levels after a certain
specific ambient N-concentration, despite the presence of high N in the medium. However, the pattern of transition varied
with the hormones applied. Further, hormones are found to affect induction of different isoforms of nitrate reductase by NH
4
+
and NO
3
−
. NH
4
+
induced isoform was prominently promoted by kinetin treatment in dark. The data documents a particular kind of interaction
between controlling factors (light, N-source and phytohormones) which affect nitrate reductase levels. 相似文献
2.
Since ferredoxin-dependent sulfite reductase (EC 1.8.7.1) and nitrite reductase (EC 1.7.7.1) can both catalyze the reduction of SO2-3 and NO?2, physiological and biochemical evidence is needed for properly classifying the two enzyme activities. They were therefore compared during ontogeny of pea leaves and in the effect of their products, sulfide and ammonium, on their catalytic activity. In the crude extract of the young second leaf of pea plants, Pisum sativum L. cv. Vatters Frühbusch, no ferredoxin-nitrite reductase activity could be detected, but ferredoxin-sulfite reductase and ATP-sulfurylase (EC 2.7.7.4), measured for comparison, were at 24 and 14%, respectively, of their maximal activity per leaf. After 11 and 12 days, respectively, ATP-sulfurylase and ferredoxin-sulfite reductase were no longer detectable, whereas ferredoxin-nitrite reductase was still at more than 30% of its maximal activity per leaf. Ferredoxin-sulfite reductase was inhibited by 50% with 18 μM and 100% with 30 μM sulfide produced by this enzyme during its assay. Sulfide at 100 μM added to the assay mixture completely inhibited ferredoxin-sulfite reductase activity in the crude extract, the 30000 g pellet and its supernatant. The same addition reduced ferredoxinnitrite reductase activity by 20% in the crude extract and by 100% in the 30000 g pellet. NH+4 at 100 μM did not affect ferredoxin-sulfite reductase or ferredoxin-nitrite reductase activity. The inhibition by sulfide and the changes in activity during ontogeny similar to ATP-sulfurylase (which catalyzes the first step of assimilatory sulfate reduction) represent biochemical and physiological evidence for the correct classification of ferredoxin-sulfite reductase. The complete inhibition of ferredoxin-nitrite reductase activity in the 30000 g pellet by S2- indicates that this activity was due to a ferredoxin-sulfite reductase. 相似文献
3.
A. Henry Latorella Susan K. Bromberg Kent Lieber James Robinson 《Journal of phycology》1981,17(2):211-214
Fifteen nitrate assimilation-deficient mutants of the euryhaline green alga, Dunaliella tertiolecta Butcher were selected by their chlorate resistance. Ten mutants, unable to grow on NO3? but able to grow on NO2?, had no detectable nitrate reductase activity. Five mutants, unable to grow on either NO3? or NO2?, had depressed levels of both nitrate and nitrite reductase. A method for assaying methyl viologen-nitrate reductase in the presence of nitrite reductase is described. 相似文献
4.
The localization of the dissimilatory sulfite reductase in Desulfovibrio desulfuricans strain Essex 6 was investigated. After treatment of the cells with lysozyme, 90% of the sulfite reductase activity was found in the membrane fraction, compared to 30% after cell rupture with the French press. Sulfite reductase was purified from the membrane (mSiR) and the soluble (sSiR) fractiion. On SDS-PAGE, both mSiR and sSiR exhibited three bands at 50, 45 and 11 kDa, respectively. From their UV/VIS properties (distinct absorption maxima at 391, 410, 583, 630 nm, enzymes as isolated) and the characteristic red fluorescence in alkaline solution, mSiR and sSiR were identified as desulfoviridin. Sulfite reductase (HSO3
-H2S) activity was reconstituted by coupling of mSiR to hydrogenase and cytochrome c
3 from D. desulfuricans. The specific activity of mSiR was 103 nmol H2 min-1 mg-1, and sulfide was the major product (72% of theoretical yield). No coupling was found with sSiR under these conditions. Furthermore, carbon monoxide was used to diferentiate between the membrane-bound and the soluble sulfite reductase. In a colorimetric assay, with photochemically reduced methyl viologen as redox mediator, CO stimulated the activity of sSiR significantly. CO had no effect in the case of mSiR. These studies documented that, as isolated, both forms of sulfite reductase behaved differently in vitro. Clearly, in D. desulfuricans, the six electron conversion HSO3
-H2S was achieved by a membranebound desulfoviridin without the assistance of artificial redox mediators, such as methyl viologen.Abbreviations
SiR
sulfite reductase
-
mSiR
sulfite reductase purified from membranes
-
sSiR
sulfite reductase purified from the soluble fraction
Enzymes Sulfite reductase, EC 1.8.99.1 Cytochrome c
3 hydrogenase, EC 1.12.2.1 相似文献
5.
Mario Klimacek Regina Kratzer Margarete Szekely 《Biocatalysis and Biotransformation》2013,31(2-4):194-201
The 2.2 Å X-ray crystal structure of Candida tenuis xylose reductase (AKR2B5) bound with NADP+ reveals that Phe-114 contributes to the substrate binding pocket of the enzyme. In the related human aldose reductase (AKR1B1), this phenylalanine is replaced by a tryptophan. The side chain of Trp was previously implicated in forming a hydrogen bond with bound substrate or inhibitor. The apparent Michaelis constant of AKR2B5 for xylose (Km≈90 mM) is 60 times that of AKR1B1, perhaps because critical enzyme–substrate interactions of Trp are not available to Phe-114. We, therefore, prepared a Phe-114→Trp mutant (F114W) of AKR2B5, to mimic the aldose reductase relationship in xylose reductase. Detailed analysis of the kinetic consequences in purified F114W revealed that the Km values for xylose and xylitol at pH 7.0 and 25°C were increased 5.1- and 4.4-fold, respectively, in the mutant compared with the wild-type. Turnover numbers (kcat) of F114W for xylose reduction and xylitol oxidation were half those of the wild-type. Apparent dissociation constants of NADH (KiNADH=44 µM) and NAD+ (KiNAD+=177 µM) were increased 1.6- and 1.4-fold in comparison with values of KiNADH and KiNAD+ for the wild-type, respectively. Catalytic efficiencies (kcat/Km) for NADH-dependent reduction of different aldehydes were between 3.1- and 31.5-fold lower than the corresponding kcat/Km values of the wild-type. Therefore, replacement of Phe-114 with Trp weakens rather than strengthens apparent substrate binding by AKR2B5, suggesting that xylose reductase exploits residue 114 in a different manner from aldose reductase. 相似文献
6.
Anuradha Hora 《Preparative biochemistry & biotechnology》2013,43(8):769-784
Hexavalent chromium contamination is a serious problem due to its high toxicity and carcinogenic effects on the biological systems. The enzymatic reduction of toxic Cr(VI) to the less toxic Cr(III) is an efficient technology for detoxification of Cr(VI)-contaminated industrial effluents. In this regard, a chromate reductase enzyme from a novel Ochrobactrum sp. strain Cr-B4, having the ability to detoxify Cr(VI) contaminated sites, has been partially purified and characterized. The molecular mass of this chromate reductase was found to be 31.53 kD, with a specific activity 14.26 U/mg without any addition of electron donors. The temperature and pH optima for chromate reductase activity were 40°C and 8.0, respectively. The activation energy (Ea) for the chromate reductase was found to be 34.7 kJ/mol up to 40°C and the activation energy for its deactivation (Ed) was found to be 79.6 kJ/mol over a temperature range of 50–80°C. The frequency factor for activation of chromate reductase was found to be 566.79 s?1, and for deactivation of chromate reductase it was found to be 265.66 × 103 s?1. The reductase activity of this enzyme was affected by the presence of various heavy metals and complexing agents, some of which (ethylenediamine tetraacetic acid [EDTA], mercaptoethanol, NaN3, Pb2+, Ni2+, Zn2+, and Cd2+) inhibited the enzyme activity, while metals like Cu2+ and Fe3+ significantly enhanced the reductase activity. The enzyme followed Michaelis–Menten kinetics with Km of 104.29 µM and a Vmax of 4.64 µM/min/mg. 相似文献
7.
Nitrate Reductase Activity in Calcifugous and Calcicolous Tomatoes as Affected by Iron Stress 总被引:1,自引:0,他引:1
Calcicolous plants are generally more Fe-efficient than calcifugous plants, because they respond to Fe stress by releasing H-ions and “reductants” from their roots that causes Fe to become available. The objective of our study was to determine if differential response to Fe stress in calcicolous and calcifugous varieties affects nitrate reductase activity. T3238FER (Fe-efficient) and T3238fer (Fe-inefficient) tomato (Lycopersicon esculentum Mill.) cultivars were grown in nutrient solutions supplied with N as NH4+-N plus NO3?-N, and as NO3?-N only. The chemical reactions induced by Fe stress concomitantly increased nitrate reductase activity in roots and tops of calcicolous, but not in calcifugous tomato. This nitrate reductase activity decreased, however, when Fe was made available to the plants. When Fe stress was eliminated by adding Fe, nitrate reductase activity was comparable in the two cultivars. 相似文献
8.
Electrostatic properties on the protein surface were examined on the basis of the crystal structure of NADH-cytochrome b5 reductase refined to a crystallographic R factor of 0.223 at 2.1 Å resolution and of the other three flavin-dependent reductases. A structural comparison of NADH-cytochrome b5 reductase with the other flavin-dependent reductases, ferredoxin-NADP+ reductase, phthalate dioxygenase reductase, and nitrate reductase, showed that the α/β structure is the common motif for binding pyridine nucleotide. Although the amino acid residues associated with pyridine nucleotide-binding are not conserved, the electrostatic properties and the location of the pyridine nucleotide-binding pockets of NADH-requiring reductases were similar to each other. The electrostatic potential of the surface near the flavin-protruding side (dimethylbenzene end of the flavin ring) of NADH-cytochrome b5 reductase was positive over a wide area while that of the surface near the heme-binding site of cytochrome b5 was negative. This implied that the flavin-protruding side of NADH-cytochrome b5 reductase is suitable for interacting with its electron-transfer partner, cytochrome b5. This positive potential area is conserved among four flavin-dependent reductases. A comparison of the electron-transfer partners of four flavin-dependent reductases showed that there are significant differences in the distribution of electrostatic potential between inter-molecular and inter-domain electron-transfer reactions. © 1996 Wiley-Liss, Inc. 相似文献
9.
Wolfgang Brüggemann Petra R. Moog Hikoki Nakagawa Peter Janiesch Pieter J. C. Kuiper 《Physiologia plantarum》1990,79(2):339-346
The properties of NADH-dependent Fe3+-EDTA reductase in plasma membranes (PM) from roots of iron-deficient and -sufficient tomato plants [Lycopersicon esculentum L. (Mill.) cv. Abunda] were examined. Iron deficiency resulted in a 3-fold increase of in vivo root iron-chelate reductase activity with a Km (Fe3+-EDTA) of 230 μM. In purified root PM, average specific activities of ferric chelate reductase of 410 and 254 nmol Fe (mg protein)?1 min?1 were obtained for iron-deficient and -sufficient plants, respectively. In both cases, the PM-bound activity showed a pH optimum at pH 6.8. Activity depended on NADH and not on NADPH and on the presence of detergent. The activity was inhibited 40-50% by superoxide dismutase (EC 1.15.1.1) and ca 30% by oxygen. Kinetic analysis of the membrane-bound enzyme revealed a Km (Fe3+-EDTA) of ca 200 μM for both iron-stressed and -sufficient plants. For NADH, Km values around 230 μM were obtained. The ferric chelate reductase could be solubilised from salt-washed PM with Triton X-100 at a protein:detergent ratio of 1:2.8 (w/w). The Triton-soluble fraction revealed one enzyme-stained band in native polyacrylamide electrophoresis. Although the membranes showed no nitrate reductase (NR; EC 1.6.6.1) activity, anti-spinach NR immunoglobulin G (IgG) recognized a 54 kDa band both in the PM and the Triton-soluble fraction, but not in the enzymatically active material obtained from the native gel. No evidence could be found for the synthesis of a new, biochemically distinct PM-bound ferric chelate reductase under iron deficiency, which might be identified as the so-called Turbo reductase. It is concluded that iron deficiency in tomato induces increased expression of a ferric chelate reductase in root PM, which is already present in iron-sufficient plants and probably also in plants, which do not contain the Turbo reductase, like the grasses. The iron reductase is not identical with the recently reported PM-associated nitrate reductase. 相似文献
10.
Molybdenum is required for induction of nitrate reductase and of NAD-linked formate dehydrogenase activities in suspensions of wild type Paracoccus denitrificans; tungsten prevents the development of these enzyme activities. The wild type forms a membrane protein M
r150,000 when incubated with tungsten and inducers of nitrate reductase and this is presumed to represent an inactive form of the enzyme. Suspensions of mutant M-1 did not develop nitrate reductase or formate dehydrogenase activities but the membrane protein M
r150,000 was formed under all conditions tested, including without inducers and without molybdenum. Analysis of membranes, solubilized with deoxycholate, by polyacrylamide gel electrophoresis under nondenaturing conditions showed that the mutant protein had similar electrophoretic mobility to the active nitrate reductase formed by the wilde type. Autoradiography of preparations from cells incubated with 55Fe showed that the mutant and wild type proteins contained iron. However, in similar experiments with 99Mo, incorporation of molybdenum into the mutant protein was not detectable.We conclude that mutant M-1 is defective in one or more steps required to process molybdenum for incorporation into molybdoenzymes. This failure affects the normal regulation of nitrate reductase protein with respect to the role of inducers.Non-Standard Abbreviations DOC
deoxycholate
- PAGE
polyacrylamide gel electrophoresis
- SDS
sodium dodecyl sulfate 相似文献
11.
Many N2-fixing organisms can turn off nitrogenase activity in the presence of NH4
+ and turn it on again when the NH4
+ is exhausted. One of the most interesting systems for accomplishing this is by covalent modification of one subunit of dinitrogenase reductase by dinitrogenase reductase ADP-ribosyltransferase (DRAT). The system can be reactivated when NH4
+ is exhausted, by dinitrogenase reductase activating glycohydrolase (DRAG) which removes the inactivating group. It is fascinating that some species of the genusAzospirillum possess the DRAT and DRAG systems (A. lipoferum andA. brasilense), whereasA. amazonense in the same genus lacks DRAT and DRAG.A. amazonense responds to NH4
+ but does not exhibit modification of dinitrogenase reductase characteristic of the action of DRAT. However, it has been possible to clone DRAT and DRAG and to introduce them intoA. amazonense, whereupon they become functional in this organism. The DRAT and DRAG system does not appear to function inAcetobacter diazotrophicus, an organism isolated from sugar cane, that fixes N2 at a pH as low as 3.0.A. diazotrophicus does show a rather sluggish response to NH4
+. A level of about 10 M NH4
+ is required to switch off the system. The response to NH4
+ is influenced by the dissolved oxygen concentration (DOC) as has been reported forAzospirillum sp. A DOC in equilibrium with 0.1 to 0.2 kPa O2 seems optimal for the response inA. diazotrophicus. 相似文献
12.
NADH:nitrate reductase (EC 1.6.6.1) from squash (Cucurbita maxima Duch., cv. Buttercup) can catalyze the reduction of a ferriphytosiderophore from barley (Hordeum vulgare L. cv. Europa). Maximal activity occurs at pH 6, with an apparentK
m
andV
max of 76 M and 21 nmol·min-1·(mg protein)-1, respectively. The ferriphytosiderophore strongly inhibits nitrate reduction catalyzed by nitrate reductase at the optimal pH for nitrate reduction, i.e. 7.5. On the contrary, nitrate is a poor inhibitor of ferriphytosiderophore reduction catalyzed by nitrate reductase at the optimal pH for this reaction, pH 6.0. Thus, squash has the potential to assimilate the iron from a ferriphytosiderophore synthesized by another plant. 相似文献
13.
Yang‐Wei Liu Kevin Denkmann Konrad Kosciow Christiane Dahl David J. Kelly 《Molecular microbiology》2013,88(1):173-188
Tetrathionate (S4O62?) is used by some bacteria as an electron acceptor and can be produced in the vertebrate intestinal mucosa from the oxidation of thiosulphate (S2O32?) by reactive oxygen species during inflammation. Surprisingly, growth of the microaerophilic mucosal pathogen Campylobacter jejuni under oxygen‐limited conditions was stimulated by tetrathionate, although it does not possess any known type of tetrathionate reductase. Here, we identify a dihaem cytochrome c (C8j_0815; TsdA) as the enzyme responsible. Kinetic studies with purified recombinant C. jejuni TsdA showed it to be a bifunctional tetrathionate reductase/thiosulphate dehydrogenase with a high affinity for tetrathionate. A tsdA null mutant still slowly reduced, but could not grow on, tetrathionate under oxygen limitation, lacked thiosulphate‐dependent respiration and failed to convert thiosulphate to tetrathionate microaerobically. A TsdA paralogue (C8j_0040), lacking the unusual His–Cys haem ligation of TsdA, had low thiosulphate dehydrogenase and tetrathionate reductase activities. Our data highlight a hitherto unrecognized capacity of C. jejuni to use tetrathionate and thiosulphate in its energy metabolism, which may promote growth in the host. Moreover, as TsdA represents a new class of tetrathionate reductase that is widely distributed among bacteria, we predict that energy conserving tetrathionate respiration is far more common than currently appreciated. 相似文献
14.
Bovine adrenodoxin was cross-linked to adrenodoxin reductase with 1-ethyl-3-(3-dimethyl-aminopropyl) carbodiimide. Mass spectrometry showed the reaction product to be a 1:1 complex of the two proteins with Mr = 64,790 ± 50. The cross-linked complex showed cytochrome c reductase activity and could be crystallized by hanging-drop vapor diffusion. Crystals of the adrenodoxin-adrenodoxin reductase complex are hexagonal, space group P6122 or P6522, with a = 93.26 Å and c= 612.20 Å and diffract to 2.9 Å resolution at 100 K. Assuming two cross-linked complexes per asymmetric unit yields a reasonable VM of 2.97 Å3/Da. Proteins 28:289–292, 1997. © 1997 Wiley-Liss Inc. 相似文献
15.
The NADH and NADPH ferricyanide reductase activities present in mitochondrial NADH-CoQ reductase preparations have been studied utilizing two photoaffinity pyridine nucleotide analogues: arylazido--alanyl NAD+ (A3-O-{3-[N-(4-azido-2-nitrophenyl)amino]propionyl}NAD+) and arylazido--alanyl NADP+ (N3-O-{3-[N-(4-azido-3-nitrophenyl)amino]-propionyl}NADP+). For the NADH-K3Fe(CN)6 reductase activity, arylazido--alanyl NAD+ was found to be, in the dark, a competitive inhibitor with respect to both NADH and K3Fe(CN)6 withK
i,app values of 9.7 and 15.5 µM, respectively. In comparison the NADP+ analogue exhibited weak noncompetitive inhibitor activity for this reaction against both substrates. Upon photoirradiation arylazido--alanyl NAD+ inhibited NADH-K3Fe(CN)6 reductase up to 70% in the presence of a 25-fold molar excess of analogue over the enzyme concentration. This photodependent inhibition could be prevented by the presence, during irradiation, of the natural substrate NADH. In contrast complex kinetic results were obtained with studies of the effects of the pyridine nucleotide analogues of NADPH-K3Fe(CN)6 reductase activity in the dark. Photoirradiation of either analogue in the presence of the enzyme complex resulted in an activation of NADPH-dependent activity. The possibility that the NADPH-K3Fe(CN)6 reductase activity of complex I represents a summation of the combined ferricyanide reductase activity of the NADPH-NAD+ transhydrogenase and NADH oxidoreductase is suggested. 相似文献
16.
17.
Yasuhiro Sagara Takayuki Hara Yasuyuki Ariyasu Fumiko Ando Naomi Tokunaga Tadao Horiuchi 《FEBS letters》1992,300(3)
Four forms of bovine adrenodoxin with modified amino-termini obtained by direct expression of cDNAs in Escherichia coli are Ad(Met1), Ad(Met−1), Ad(Met−12), and Ad(Met6). The shoulder numbers represent this site of translation initiator Met at the amino-termini. The adrenodoxins, except for Ad(Met−1), were purified from the cell lysate and the ratios of A414-to-A276 of the purified proteins were over 0.92. NADPH-cytochrome c reductase activities of the three forms of adrenodoxin in the presence of adrenodoxin reductase were the same as that of purified bovine adrenocortical adrenodoxin. However, as cytochrome P-450SCC reduction catalyzed by Ad(Met0) was about 60% or that by Ad(Met1), the contribution of the amino-terminal region for the electron transfer or binding to cytochrome P-450SCC would need to be considered. 相似文献
18.
Summary Wild-type pneumococci derived from Avery's strain R36A are sensitive to extracellular concentrations of the folate antimetabolite aminopterin exceeding 1.0x10-6
M. Three classes of resistant strains are phenotypically distinguishable: amiB-r, amiA-r and amiD-r strains are resistant to low (1.5x10-6
M), intermediate (0.5–4.0×10-5
M) and high (4.5x10-4
M) aminopterin levels respectively. The amiA and amiB regions are weakly linked, but linkage has not been established between either of these loci and the amiD region.Consistent with the maximum resistance conferred by mutations in the amiA locus, dihydrofolate (FH2) reductase in cell-free extracts (CFE) of amiA-r strains has a two- to six-fold greater affinity for the substrate than dose the enzyme in wild-type CFE (Table 1); FH2 reductase from amiA-r strains may also have reduced affinity for aminopterin. Specific activity of the enzyme is not affected by mutation in the amiA locus (Table 1) and its affinity for the cofactor (NADPH) is probably unaffected by mutation in this locus (Table 4). Dihydrofolate reductase activity in amiA5 CFE is considerably more thermolabile than that in wild-type CFE (Table 2).The enzyme in CFE of the high resistance strain amiD1 has the same affinity for the substrate, cofactor and antimetabolite as FH2 reductase in wild-type CFE (Figs. 1–4, 8 and 9; Table 4). However, specific activity of the enzyme in amiD1 CFE is 11-fold higher than that in wild-type CFE (Table 1) and it is much more heat stable (Table 2).Some properties of FH2 reductase in CFE of the high resistance recombinant strain amiA5amiD1 are intermediate between those in CFE of wild-type and amiD1.Preliminary results suggest that CFE of wild-type and amiA5 contain a factor, which is neither dialyzable nor heat sensitive, that has an inhibitory effect upon activity and stability of FH2 reductase in amiD1 CFE (Tables 2 and 3). 相似文献
19.
The location of the dissimilatory nitrite reductase and orientation of its reducing site of the Grampositive denitrifier, Bacillus firmus NIAS 237 were examined. Approximately 90% of the total dissimilatory nitrite reductase activity with ascorbate-reduced phenazine methosulfate (PMS) as the electron donor was on the protoplast membrane. Nitrite induced with intact Bacillus cells an alkalinization in the external medium, followed by acidification. The electron transfer inhibitor, 2-heptyl-4-hydroxyquinoline-N-oxide, which blocked nitrite reduction with endogenous substrates, inhibited the acidification, but not the alkalinization. Alkalinization was not affected with ascorbate-reduced PMS as the artificial electron donor. This indicated that the alkalinization is not associated with proton consumption outside the cytoplasmic membrane by the extracellular nitrite reduction. The dissimilatory nitrite reductase of B. firmus NIAS 237 was located on the cytoplasmic membrane, and its reducing site is suggested to be on the inner side of this membrane.Abbreviations CCCP
carbonylcyanide m-chlorophenylhydrazone
- HOQNO
2-heptyl-4-hydroxyquinoline-N-oxide
- PMS
phenazine methosulfate
- H+/NO
inf2
sup-
ratio
number of consumed protons in the external medium per one ion of NO
inf2
sup-
reduced 相似文献
20.
Ayala Hochman 《Archives of microbiology》1982,133(1):62-65
Nitrate reduction was studied in the dinoflagellatePeridinium cinctum collected from extensive algal blooms in Lake Kinneret (Israel).Among several methods tested for the preparation of cell free extracts, only the use of a ground-glass tissue culture homogenizer was found to be efficient. The assimilatory nitrate reductase ofP. cinctum was located in a particulate fraction. In this respect,P. cinctum did not behave like other eukaryotes, such as green algae, but as a prokaryote. Nitrite reductase activity was found in the soluble fraction.Nitrate reductase used NADH as a preferable electron donor; it reacted also with NADPH but only to give 16.5% of the NADH dependent rate. Methyl viologen and benzyl viologen could also serve as electron donors, with rates higher than the NADH dependent activity (3–6 times and 1.5–3 times, respectively). The Km of nitrate reductase for NADH was 2.8×10–4 M and for NO3-1.9×10–4 M. Flavins did not stimulate the activity, nor was ferricyanide able to activate it. Carboxylic anions stimulated nitrate reductase activity 3–4 fold, an effect which was not mimicked by other anions.Chlorate, azide and cyanide were competitive inhibitors ofP. cinctum, nitrate reductase withK
i values of 1.79×10–3 M, 2.1×10–5 M and 8.9×10–6 M respectively. 相似文献