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1.
Assaying for pyruvate,orthophosphate dikinase activity: Necessary precautions with phosphoenolpyruvate carboxylase as coupling enzyme 总被引:1,自引:0,他引:1
Phosphoenolpyruvate carboxylase (EC 4.1.1.31), used as a coupling enzyme in the assay of the pyruvate, orthophosphate dikinase (EC 2.7.9.1) forward reaction, is a serious limiting factor for the overall rate when added at a level of 0.2–0.3 unit/ml of assay medium. Nonlimiting assay conditions are obtained by either increasing the level of the coupling enzyme to 3 units/ml or adding 6mM glucose-6-phosphate as an activator/stabilizer of phosphoenolpyruvate carboxylase.Abbreviations G-6-P
glucose-6-phosphate
- LDH
lactate dehydrogenase
- MDH
malate dehydrogenase
- PEP
phosphoenolpyruvate
- PEPCase
phosphoenolpyruvate carboxylase
- PVP
polyvinylpyrrolidone
- PPDK
pyruvate, orthophosphate dikinase
- U
unit of enzyme activity (mol/min) 相似文献
2.
The activities of phosphoenolpyruvate carboxylase (PEP carboxylase, EC 4.1.1.3.1) have been investigated in various organs of young nodulated Alnus glutinosa. The root nodules exhibited the highest specific enzyme activity when compared with the one in roots and leaves. Furthermore, in the root nodules the PEP carboxylase was predominantly localized in the cytosol of the large cortical cells containing the endophyte vesicles.Abbreviations PEP carboxylase
phosphoenolpyruvate carboxylase
- MDH
malate dehydrogenase
- PVP
polyvinylpyrrolidone
- PBS
phosphate buffer saline 相似文献
3.
A malate dehydrogenase (MDH) was characterized from the cyanobacterium Coccochloris peniocystis. The enzyme was purified approximately 180-fold and had a molecular weight of about 90000. The enzyme had a pH optimum of pH 6.7 to 7.5; a Km (malate) of 5.6 mM and Kms for NAD and NADP of 24 M and 178 M, respectively, although similar Vmax were obtained with either pyridine nucleotide. Enzyme activity was inhibited by ATP, citrate, oxalacetate, acetyl CoA and CoA. Enzyme assays with uniformly 14C-labelled malate caused no 14CO2 release, indicating this MDH is not a malic enzyme. Electrophoresis and S-200 gel filtration of the partially purified enzyme indicated a single MDH was present in this preparation. A second, less abundant, MDH was present in crude extracts. The presence of MDH in this organism is consistent with the operation of a glyoxylate cycle which, in the absence of a TCA cycle, would provide organic acids required in secondary carbon metabolism. ATP inhibition of MDH may allow for light regulation of MDH activity since, in the light, oxaloacetic acid is generated by phosphoenolpyruvate carboxylase activity.Abbreviations MDH
malate dehydrogenase
- PEPcase
phosphoenolpyruvate carboxylase
- MOPS
3-[N-Morpholino] propane sulfonic acid
- TRIS
Tris(hydroxymethyl)-aminomethane
- EDTA
Disodium Ethylenadiamine Tetraacetate
- MES
2[N-Morpholino]-ethane Sulfonic Acid
- EPPS
N-2-Hydroxyethylpiperazine Propane
- MW
Molecular weight
- OAA
Oxaloacetic acid 相似文献
4.
Evidence for chloroplastic localization of spinach leaf NADP malate dehydrogenase activating factors
Dithiothreitol activation of spinach leaf NADP malate dehydrogenase is mediated by protein factors that have been partially purified by chromatography on DEAE cellulose. Evidence for their intrachloroplastic localization has been obtained.Abbreviations DTT
dithiothreitol
- MDH
malate dehydrogenase 相似文献
5.
Phosphoenolpyruvate carboxylase from leaves of the C4 plant Setaria verticillata (L.) Beauv. is activated by light; day levels of activity are reached after 30 minutes of illumination. Photoactivation is prevented by inhibitors of photosynthetic electron flow or of photophosphorylation and by D,L-glyceraldehyde, which inhibits the reductive pentose phosphate pathway.Although the extractable activity in the dark is not affected by temperature the photoactivation is prevented when both illumination and extraction are done under low temperature (5 C). High temperature (30 C) during either illumination or extraction is needed for activation. Once the enzyme is photoactivated at 30 C, a transfer of the leaves to 5 C does not abolish the extra activity.The results suggest that both unimpaired electron flow and photophosphorylation are prerequisites for the activation of phosphoenolpyruvate carboxylase. Low temperature apparently suppresses either the transport to the cytoplasm of a photosynthetic intermediate or the activating reaction itself. The inclusion of phosphoenolpyruvate in the extraction medium increases the night activity.On the basis of the available information, it is suggested that phosphoenolpyruvate could be the activator in vivo. In that case, the activation of phosphoenolpyruvate carboxylase would depend on internal CO2 level and prior photoactivation of both pyruvate, orthophosphate, dikinase and NADP malate dehydrogenase.Abbreviations PEPCase
phosphoenolpyruvate carboxylase
- PEP
phosphoenolpyruvate
- PAR
photosynthetically active radiation
- CCCP
carbonyl cyanide m-chlorophenylhydrazone
- DCMU
3-(3, 4-dichlorophenyl)-1, 1-dimethylurea
- DSPD
disalicylidenpropanediamine
- MV
methylviologen
- ME
malic enzyme
- MDH
malate dehydrogenase
- PPDK
pyruvate, Pi dikinase
- CAM
Crassulacean Acid Metabolism 相似文献
6.
Summary Some photosynthetic and biochemical properties of the chlorophyl containing layers of the pericarp of developing barley have been investigated. The tissue changes from pale green to bright green early in development, chlorophyll disappearing only at the later stages of maturity. It contains chloroplasts and probably amyloplasts and starch bearing chloroplasts. It is capable of high rates of light dependent oxygen evolution. It has been shown that the enzyme phosphoenol pyruvate carboxylase (EC 4.1.1.31) is present in the pericarp and is 100 times as active in carbon dioxide fixation as ribulose diphosphate carboxylase (EC 4.1.1.39). Other enzymes present in the pericarp are phosphoenol pyruvate synthetase, pyrophosphatase (EC 3.6.1.1), malate NAD and NADP dehydrogenases (EC 1.1.1.37), malic enzyme (EC 1.1.1.40), and fructose 1,6 diphosphatase (EC 3.1.3.11).Abbreviations RDP
Ribulose 1,5-diphosphate
- PEP
phosphoenol pyruvate 相似文献
7.
Summary An albino seedling of Zea mays L. was investigated for its potential for CO2-assimilation. In the mesophyll the number, dimensions and fine structure of chloroplasts are drastically reduced but to a lesser extent in the bundle sheath. Chlorophyll concentration is zero and carotenoid concentration almost zero. Albinism also exerts a strong influence on the stroma of bundle sheath chloroplasts; ribulose-1.5-biphosphate carboxylase (EC 4.1.1.39) activity and glyceraldehyde-3-phosphate dehydrogenase (NADP) (EC 1.2.1.13) activity is not detectable. The C4-enzymes phosphoenolpyruvate carboxylase (EC 4.1.1.31) and malate dehydrogenase (decarboxylating) (EC 1.1.1.40) and the non-photosynthetic linked enzymes malate dehydrogenase (NAD) (EC 1.1.1.37), aspartate-2-oxoglutarate aminotransferase (EC 1.1.1.37), aspartate-2-oxoglutarate aminotransferase (EC 2.6.1.1.) and glyceraldehyde-3-phosphate dehydrogenase (NAD) (EC 1.2.1.1.) are present in the albino seedling with activities comparable to those in etiolated maize seedlings. The potential for CO2 fixation of the albino seedlings exceeds that of comparable dark seedlings considerably. The results are discussed with regard to enzyme localization of the C4 pathway of photosynthesis.Abbreviations Aspartate aminotransferase
L-aspartate-2-oxoglutarate aminotransferase-EC 2.6.1.1.
- GAPDH (NAD)
glyceraldehyde-3-phosphate dehydrogenase (NAD dep.)-EC 1.2.1.12
- GAPDH (NADP)
glyceraldehyde-3-phosphate dehydrogenase (NADP dep.)-EC 1.2.1.13
- malic enzyme
malate dehydrogenase (NADP dep., decarboxylating)-EC 1.1.1.40
- MDH
malate dehydrogenase (NAD dep.)-1.1.1.37
- PEP carboxylase
phosphoenolpyruvate carboxylase-EC 4.1.1.31
- RuDP carboxylase
ribulose-1.5-biphosphate carboxylase-EC 4.1.1.39 相似文献
8.
O. Pines S. Shemesh E. Battat I. Goldberg 《Applied microbiology and biotechnology》1997,48(2):248-255
Saccharomyces cerevisiae accumulates l-malic acid through a cytosolic pathway starting from pyruvic acid and involving the enzymes pyruvate carboxylase and malate
dehydrogenase. In the present study, the role of malate dehydrogenase in the cytosolic pathway was studied. Overexpression
of cytosolic malate dehydrogenase (MDH2) under either the strong inducible GAL10 or the constitutive PGK promoter causes a
6- to 16-fold increase in cytosolic MDH activity in growth and production media and up to 3.7-fold increase in l-malic acid accumulation in the production medium. The high apparent K
m of MDH2 for l-malic acid (11.8 mM) indicates a low affinity of the enzyme for this acid, which is consistent with the cytosolic function
of the enzyme and differs from the previously published K
m of the mitochondrial enzyme (MDH1, 0.28 mM). Under conditions of MDH2 overexpression, pyruvate carboxylase appears to be
a limiting factor, thus providing a system for further metabolic engineering of l-malic acid production. The overexpression of MDH2 activity also causes an elevation in the accumulation of fumaric acid and
citric acid. Accumulation of fumaric acid is presumably caused by high intracellular l-malic acid concentrations and the activity of the cytosolic fumarase. The accumulation of citric acid may suggest the intriguing
possibility that cytosolic l-malic acid is a direct precursor of citric acid in yeast.
Received: 22 January 1997 / Received revision: 14 April 1997 / Accepted: 19 April 1997 相似文献
9.
Glycerol stabilizes the activity of pyruvate, orthophosphate dikinase extracted from darkened or illuminated maize leaves. It serves as a better protectant of activity than dithiothreitol for the active day-form and the glycerol concentration needed for full protection is inversely related to the level of protein. The night-form of the enzyme is also protected by glycerol not only against inactivation, but also against partial reactivation in storage. Glycerol does not prevent the Pi-dependent activation nor the ADP-dependent inactivation of pyruvate, orthophosphate dikinase, but the rates of both processes are substantially decreased. The ability of the inactive night-form for Pi-dependent activation is also sustained by glycerol for at least 2 h at 20°C, apparently through stabilization of the labile regulatory protein.Abbreviations BSA
bovine serum albumin
- G-6-P
glucose-6-phosphate
- MDH
malate dehydrogenase
- PCMB
p-chloromercuribenzoate
- PEP
phosphoenolpyruvate
- PEPCase
phosphoenol-pyruvate carboxylase
- PPDK
pyruvate, orthophosphate dikinase
- PVP
polyvinylpyrrolidone 相似文献
10.
A. Aidoo R. J. Feuers L. E. Lyn-Cook M. E. Bishop D. A. Casciano 《Cell biology and toxicology》1996,12(2):79-87
Efficient energy utilization is essential for cell growth; in an attempt to improve the growth conditions of the rat T-lymphocyte culture model for potential use in studying the mutagenic activity of carcinogens in vitro, we have investigated the effects of phytohemagglutinin (PHA), interleukin-2 (IL-2) and 2-mercaptoethanol (2-ME) on the activities of intermediary metabolism enzymes and cell proliferation. Isolated lymphocytes were cultured in the presence and absence of PHA, IL-2, or 2-ME. The intermediary metabolism enzymes investigated were glutamate dehydrogenase, glutamate-pyruvate transaminase, malate dehydrogenase, isocitrate dehydrogenase, lactate dehydrogenase, pyruvate kinase, and fatty acid synthetase (FAS). Measurable activity of all enzymes investigated, except for FAS, was detected in PHA-stimulated cells cultured with IL-2 or 2-ME. The unstimulated lymphocytes had significantly lower enzyme activity than stimulated cells. The combination of all three agents showed increased enzyme activity. This increase in activity brought about by the combination of the three agents was not reproduced by either agent acting alone. In general, the increase in enzyme activity correlated with cell proliferation as measured by [3H]thymidine uptake in PHA-stimulated cultures containing IL-2 and/or 2-ME. The results suggest that the addition of exogenous IL-2 and 2-ME enhances metabolic function and may be beneficial in in vitro culture of rat lymphocytes.Abbreviations PHA
phytohemagglutinin
- IL-2
interleukin-2
- 2-ME
2-mercaptoethanol
- GDH
glutamate dehydrogenase
- GPT
glutamate-pyruvate transaminase
- MDH
malate dehydrogenase
- ICD
isocitrate dehydrogenase
- LDM
lactate dehydrogenase
- PK
pyruvate kinase
- FAS
fatty acid synthetase 相似文献
11.
Kalanchoë pinnata mitochondria readily oxidized succinate, malate, NADH, and NADPH at high rates and coupling. The highest respiration rates usually were observed in the presence of succinate. The high rate of malate oxidation was observed at pH 6.8 with thiamine pyrophosphate where both malic enzyme (ME) and pyruvate dehydrogenase were activated. In CAM phase III of K. pinnata mitochondria, both ME and malate dehydrogenase (MDH) simultaneously contributed to metabolism of malate. However, ME played a main function: malate was oxidized via ME to produce pyruvate and CO2 rather than via MDH to produce oxalacetate (OAA). Cooperative oxidation of two or three substrates was accompanied with the dramatic increase in the total respiration rates. Our results showed that the alternative (Alt) pathway was more active in malate oxidation at pH 6.8 with CoA and NAD+ where ME operated and was stimulated, indicating that both ME and Alt pathway were related to malate decarboxylation during the light. In K. pinnata mitochondria, NADH and NADPH oxidations were more sensitive with KCN than that with succinate and malate oxidations, suggesting that these oxidations were engaged to cytochrome pathway rather than to Alt pathway and these capacities would be desirable to supply enough energy for cytosol pyruvate orthophosphate dikinase activity. 相似文献
12.
Acclimation of white lupin to phosphorus deficiency involves enhanced expression of genes related to organic acid metabolism 总被引:11,自引:2,他引:9
Uhde-Stone Claudia Gilbert Glena Johnson Jane M-F Litjens Ralph Zinn Kelly E. Temple Stephen J. Vance Carroll P. Allan Deborah L. 《Plant and Soil》2003,248(1-2):99-116
White lupin (Lupinus albus L.) acclimates to phosphorus deficiency (–P) by the development of short, densely clustered lateral roots called proteoid (or cluster) roots. These specialized plant organs display increased exudation of citric and malic acid. The enhanced exudation of organic acids from P stressed white lupin roots is accompanied by increased in vitro phosphoenolpyruvate carboxylase (PEPC) and malate dehydrogenase (MDH) activity. Here we report the cloning of full-length white lupin PEPC and MDH cDNAs. RNA blot analysis indicates enhanced expression of these genes in –P proteoid roots, placing higher gene expression at the site of organic acid exudation. Correspondingly, macroarray analysis of about 1250 ESTs (expressed sequence tags) revealed induced expression of genes involved in organic acid metabolism in –P proteoid roots. In situ hybridization revealed that PEPC and MDH were both expressed in the cortex of emerging and mature proteoid rootlets. A C3 PEPC protein was partially purified from proteoid roots of P deficient white lupin. Native and subunit Mr were determined to be 440 kD and 110 kD, respectively. Citrate and malate were effective inhibitors of in vitro PEPC activity at pH 7. Addition of ATP partially relieved inhibition of PEPC by malate but had little effect on citrate inhibition. Taken together, the results presented here suggest that acclimation of white lupin to low P involves modified expression of plant genes involved in carbon metabolism. 相似文献
13.
Malate valves act as powerful systems for balancing the ATP/NAD(P)H ratio required in various subcellular compartments in plant cells. As components of malate valves, isoforms of malate dehydrogenases (MDHs) and dicarboxylate translocators catalyse the reversible interconversion of malate and oxaloacetate and their transport. Depending on the co‐enzyme specificity of the MDH isoforms, either NADH or NADPH can be transported indirectly. Arabidopsis thaliana possesses nine genes encoding MDH isoenzymes. Activities of NAD‐dependent MDHs have been detected in mitochondria, peroxisomes, cytosol and plastids. In addition, chloroplasts possess a NADP‐dependent MDH isoform. The NADP‐MDH as part of the ‘light malate valve’ plays an important role as a poising mechanism to adjust the ATP/NADPH ratio in the stroma. Its activity is strictly regulated by post‐translational redox‐modification mediated via the ferredoxin‐thioredoxin system and fine control via the NADP+/NADP(H) ratio, thereby maintaining redox homeostasis under changing conditions. In contrast, the plastid NAD‐MDH (‘dark malate valve’) is constitutively active and its lack leads to failure in early embryo development. While redox regulation of the main cytosolic MDH isoform has been shown, knowledge about regulation of the other two cytosolic MDHs as well as NAD‐MDH isoforms from peroxisomes and mitochondria is still lacking. Knockout mutants lacking the isoforms from chloroplasts, mitochondria and peroxisomes have been characterised, but not much is known about cytosolic NAD‐MDH isoforms and their role in planta. This review updates the current knowledge on MDH isoforms and the shuttle systems for intercompartmental dicarboxylate exchange, focusing on the various metabolic functions of these valves. 相似文献
14.
S B Senkevich S A Strumilo I B Zavodnik V V Vinogradov 《Biokhimii?a (Moscow, Russia)》1986,51(9):1534-1540
Malate dehydrogenase from bovine adrenal cortex has been purified to homogeneity, using affinity chromatography on 2',5'-ADP-Sepharose 4B. The kinetic data do not contradict the consecutive mechanism of the reaction with the ordered addition of substrates: NADP binds first, then malate. The enzyme conformation initiated by NADP and malate binding is less thermostable. Malate dehydrogenase has intrinsic tryptophan fluorescence with the spectrum maximum at 335 +/- 1 nm, half-width of 50 +/- 1 nm and quantum yield of 0.08. The tryptophan residues belonging to class 1 (75%) and class 2 (25%) make the main contribution to the intrinsic fluorescence of malate. The binding of cofactors and substrates results in the quenching of enzyme fluorescence. The values of dissociation constants for malate dehydrogenase complexes with NADP (4 microM), with NADP . H (8 microM) and with pyruvate (2.5 mM) correlate with the corresponding values of Km. The shifts in pH of the medium induce changes in the fluorescence parameters which are probably related to conformational changes in the enzyme molecule. The changes in the fluorescence parameters correlate with the alterations of the malate dehydrogenase enzymatic activity. 相似文献
15.
Glycolysis shows different patterns of operation and different control steps, depending on whether the level of Crassulacean acid metabolism (CAM) is low or high in the leaves of Kalanchoe blossfeldiana v.Poelln., when subjected to appropriate photoperiodic treatments: at a low level of CAM operation all the enzymes of glycolysis and phosphoenol pyruvate (PEP) carboxylase present a 12 h rhythm of capacity, resulting from the superposition of two 24h rhythms out of phase; phosphofructokinase appears to be the main regulation step; attainment of high CAM level involves (1) an increase in the peak of capacity occurring during the night of all the glycolytic enzymes, thus achieving an over-all 24h rhythm, in strict allometric coherence with the increase in PEP carboxylase capacity, (2) the establishment of different phase relationships between the rhythms of enzyme capacity, and (3) the control of three enzymic steps (phosphofructokinase, the group 3-P-glyceraldehyde dehydrogenase — 3-P-glycerate kinase, and PEP carboxylase). Results show that the hypothesis of allosteric regulation of phosphofructokinase (by PEP) and PEP carboxylase (by malate and glucose-6-P) cannot provide a complete explanation for the temporal organization of glycolysis and that changes in the phase relationships between the rhythms of enzyme capacity along the pathway and a strict correlation between the level of PEP carboxylase capacity and the levels of capacity of the glycolytic enzymes are important components of the regulation of glycolysis in relation to CAM.Abbreviations CAM
crassulacean acid metabolism
- F-6-P
fructose-6-phosphate
- F-bi-P
fructose-1,6 biphosphate
- G-3-PDH
3-phosphoglyceraldehyde dehydrogenase (NAD), EC 1.2.1.12
- G-6-P
glucose-6-phosphate
- GSH
reduced glutathion
- GDH
glycerolphosphate dehydrogenase, EC 1.1.1.8
- PEP
phosphoenol pyruvate
- PEPC
PEP carboxylase, EC 4.1.1.31
- PFK
phosphofructokinase, EC 2.7.1.11
- 2-PGA
2-phosphoglycerate
- 3-PGA
3-phosphoglycerate
- PGM
phosphoglycerate phosphomutase, EC 5.4.2.1
- T.P.
triose phosphates
- TPI
triose phosphate isomerase, EC 5.3.1.1 相似文献
16.
Activities of some key enzymes of carbon metabolism sucrose synthase, acid and alkaline invertase, phosphoenol pyruvate carboxylase,
malic enzyme and isocitrate dehydrogenase were investigated in relation to the carbohydrate status in lentil pods. Sucrose
remained the dominant soluble sugar in the pod wall and seed, with hexoses (glucose and fructose) present at significantly
lower levels. Sucrose synthase is the predominant sucrolytic enzyme in the developing seeds of lentil (Lens culinaris L.). Acid invertase was associated with pod elongation and showed little activity in seeds. Sucrose breakdown was dominated
by alkaline invertase during the development of podwall, while both the sucrose synthase and alkaline invertase were active
in the branch of inflorescence. A substantial increase of sucrolytic enzymes was observed at the time of maximum seed filling
stage (10–20 DAF) in lentil seed. The pattern of activity of sucrose synthase highly paralleled the phase of rapid seed filling
and therefore, can be correlated with seed sink strength. It seems likely that the fruiting structures of lentil utilize phosphoenol
pyruvate carboxylase for recapturing respired carbon dioxide. Higher activities of isocitrate dehydrogenase and malic enzyme
in the seed at the time of rapid seed filling could be effectively linked to the deposition of protein reserves. 相似文献
17.
Malic enzyme (ME=L-malate: NADP oxidoreductase; E.C. 1.1.1.40) was extracted by Triton X-100-induced resolubilization of enzyme proteins which denaturize spontaneously upon homogenization of grape berry material. The purification procedure included fractionating with (NH4)2SO4, preparative IEF, and Sephadex G-100 chromatography. ME was identified by TLC of the radioactive product after supplementing the assay mixture with [14C]malate. Cofactor dependence, pH-optimum and affinities for substrates and cosubstrates were determined. Enzymic pI was found to be 5.8, the Hill coefficients range from 1 to 3. In malate decarboxylating direction at pH 7.4, grape ME displayed positive cooperativity toward the substrate, the curve approaching normal Michaelis-Menten-kinetics at pH 7.0. Substituting Mn2+ for Mg2+ not only increased maximal turnover rates, but also enzymic affinity for malate. These features were considered indicative of the regulatory properties of the enzyme. Their relevance for grape malate metabolism and fruit ripening is discussed.Abbreviations EDTA
ethylenediaminetetraacetic acid
- IFF
isoelectric focusing
- MDH
malate dehydrogenase
- ME
malic enzyme
- OAA
oxaloacetic acid
- PAG
polyacrylamide gel
- TCA
trichloroacetic acid
- TLC
thin layer chromatography 相似文献
18.
Kalanchoe blossfeldiana plants grown under long days (16 h light) exhibit a C3-type photosynthetic metabolism. Switching to short days (9 h light) leads to a gradual development of Crassulacean acid metabolism (CAM). Under the latter conditions, dark CO2 fixation produces large amounts of malate. During the first hours of the day, malate is rapidly decarboxylated into pyruvate through the action of a cytosolic NADP+-or a mitochondrial NAD+-dependent malic enzyme. Mitochondria were isolated from leaves of plants grown under long days or after treatment by an increasing number of short days. Tricarboxylic acid cycle intermediates as well as exogenous NADH and NADPH were readily oxidized by mitochondria isolated from the two types of plants. Glycine, known to be oxidized by C3-plant mitochondria, was still oxidized after CAM establishment. The experiments showed a marked parallelism in the increase of CAM level and the increase in substrate-oxidation capacity of the isolated mitochondria, particularly the capacity to oxidize malate in the presence of cyanide. These simultaneous variations in CAM level and in mitochondrial properties indicate that the mitochondrial NAD+-malic enzyme could account at least for a part of the oxidation of malate. The studies of whole-leaf respiration establish that mitochondria are implicated in malate degradation in vivo. Moreover, an increase in cyanide resistance of the leaf respiration has been observed during the first daylight hours, when malate was oxidized to pyruvate by cytosolic and mitochondrial malic enzymes.Abbreviations CAM
Crassulacean acid metabolism
- MDH
malate dehydrogenase
- ME
malic enzyme 相似文献
19.
Plants develop strategies to recycle phosphorus so that all organs receive adequate amounts of phosphorus, especially new
growing organs. To evaluate the metabolic adaptation of rice plants under phosphorus deficient conditions, we selected several
genes related to phosphorus utilization efficiency in the cell. Phosphoenolpyruvate carboxylase, triose phosphate translocator, phosphoenolpyruvate/phosphate translocator (PPT), pyruvate kinase, NAD dependent glyceraldehyde-3-phosphate dehydrogenase, and NADP dependent
glyceraldehyde-3-phosphate dehydrogenase were selected because of their important roles in phosphorus utilization by the cell,
and because they are part of the proposed bypass pathways by which the cells save phosphate. The most dramatic change was
observed in the expression level of PPT (which transports phosphoenolpyruvate (PEP) from the cytosol into the chloroplast); thus we believe that PEP may play an important role in maintaining
carbon metabolism under phosphate deficient conditions. 相似文献
20.
S B Senkevich 《Biokhimii?a (Moscow, Russia)》1988,53(11):1783-1790
An electrophoretically homogeneous preparation of mitochondrial NADP-dependent malate dehydrogenase with a specific activity of 155 u./mg and a 67% yield has been obtained, using ammonium sulfate fractionation, gel filtration through Toyopearl HW-55 F, ion-exchange chromatography on DEAE-Toyopearl 650 M and affinity chromatography on 2',5'-ADP-Sepharose 4B. The molecular mass of native malate dehydrogenase is 260 kD; Mr of the SDS-treated enzyme is 61 kD, which is suggestive of a tetrameric structure of the protein. Malate dehydrogenase is active only in the presence of Mg2+ or Mn2+, but not Ca2+ or Ba2+. The Km' values for Mn2+ and Mg2+ are 50 and 66 microM, respectively. At low malate concentrations and NADP saturation, the enzyme is characterized by a sigmoidal kinetics which changes to hyperbolic at low concentrations of NADP. The Lineweaver--Burk plots for the dependence of the initial reaction rate on the concentration of one substrate at several fixed concentrations of the other substrate intersect to the left of the B-axis. NADPH competes with NADP:pyruvate inhibits malate dehydrogenase ++noncompetitively with respect to the coenzyme. NADPH and pyruvate inhibit the malate dehydrogenase-catalyzed reaction via a mixed type mechanism with respect to malate. The data obtained are consistent with a consecutive mechanism of reaction, whose first substrate is NADP and the last product is NADPH. 相似文献