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1.
Enzymes essential to the operation of the Embden-Meyerhof glycolytic pathway, the Entner-Doudoroff pathway and oxidative pentose phosphate pathway were present in Thiobacillus A2 grown on glucose and other sugars. Radiorespirometry under various conditions with Thiobacillus A2 oxidising glucose specifically labelled with 14C in carbon atoms 1, 2, 3, 3+4, 6 or universally labelled demonstrated the simultaneous operation of the Embden-Meyerhof (48%), Entner-Doudoroff (28%), and pentose phosphate (24%) pathways in release of carbon dioxide from glucose. Growth on succinate, or autotrophically on formate or thiosulphate resulted in repression of most enzymes of the pathways, but high aldolase levels were retained indicating its role in gluconeogenesis and the Calvin cycle. Different fructose diphosphatase activities were found in succinate- and thiosulphate-grown organisms. The results indicate that all three major catabolic pathways for glucose function in Thiobacillus A2 grown on sugars. Thiobacillus acidophilus showed a different radiorespirometric pattern and apparently used the Entner-Doudoroff (64.5%) and pentose phosphate (35.5%) pathways, but showed unusually high release of carbon atom 6, as was also found for T. ferrooxidans.Abbreviations EM
Embden-Meyerhof
- ED
Entner-Doudoroff
- EDTA
ethylene diamine tetra-acetic acid, disodium salt
- FDP
fructose 1,6-diphosphate
- KDPG
2-keto-3-deoxy-6-phosphogluconate
- 6-PG
6-phosphogluconate
- Pa
Pascal (105 Pa=1 bar)
- PP
pentose phosphate
- POPOP
1,4-di[2-(5-phenyloxazolyl)] benzene
- PPO
2,5-diphenyloxazole 相似文献
2.
Margit Sára Karin Moser-Thier Ursula Kainz Uwe B. Sleytr 《Archives of microbiology》1990,154(3):209-214
High resolution 13C NMR combined with chemical analysis were used to study the formation of metabolites from [1-13C]-labelled glucose by the salt-tolerant yeast Debaryomyces hansenii after transfer to media containing 8% NaCl. Time course spectroscopy of an aerobic cell suspension showed [1,3-13C]glycerol as the predominant end product. Perchloric acid extracts revealed additional less prominent incorporation of label into arabinitol, trehalose, glutamic acid, and alanine. The incorporation into trehalose and arabinitol showed a transient increase after shift to the high salinity medium. It is concluded that glycerol and arabinitol are the major organic solutes in D. hansenii, the production of glycerol being strongly induced by high salinity. Analysis of labelled extracts of D. hansenii after transfer to 8% NaCl media containing [1-13C]- or [6-13C]glucose, demonstrated that glucose is dissimilated via a combination of the Embden-Meyerhof-Parnas pathway and the pentose phosphate pathway, with the former playing a major role in glycerol formation and the latter in arabinitol production. The almost exclusive labelling of C5 of arabinitol from [6-13C]glucose indicates that the pathway to arabinitol proceeds via reduction of ribulose-5-phosphate.Abbreviations used NMR
nuclear magnetic resonance
- EMP
Emden-Meyerhof-Parnas
- PP
pentose phosphate
- GAP
glyceraldehyde phosphate
- DHAP
dihydroxyacetone phosphate
- ppm
parts per million 相似文献
3.
Summary We did this work to see if there is a correlation between lignin synthesis and the activity of the pentose phosphate pathway. Excision of the third internode of the stem of Coleus blumei Benth. followed by incubation on sucrose and indoleacetic acid led to extensive formation of tracheids. During this lignification we determined the activities of glucose-6-phosphate dehydrogenase and fructose-1,6-diphosphate aldolase, and the extent to which [1-14C]-,[3,4-14C]-, and [6-14C]glucose labelled CO2 and the major cellular components. The results indicate that the pentose phosphate pathway was active during lignification, and that the activity of this pathway relative to glycolysis increased at the onset of lignification. Explants of storage tissue of Helianthus tuberosus L. were cultured under conditions which caused extensive lignification. 14CO2 production from [1-14C]-, [3,4-14C]-, and [6-14C]glucose indicated activity of the pentose phosphate pathway during tracheid formation. We suggest that lignification is accompanied by appreciable activity of the pentose phosphate pathway and that this could provide the reducing power for lignin synthesis.Abbreviations NADP
nicotinamide-adenine dinucleotide phosphate
- IAA
indoleacetic acid 相似文献
4.
Gluconobacter oxydans was grown successively in glucose and nitrogen-limited chemostat cultures. Construction of mass balances of organisms growing at increasing dilution rates in glucose-limited cultures, at pH 5.5, revealed a major shift from extensive glucose metabolism via the pentose phosphate pathway to the direct pathway of glucose oxidation yielding gluconic acid. Thus, whereas carbon dioxide production from glucose accounted for 49.4% of the carbon input at a dilution rate (D)=0.05 h-1, it accounted for only 1.3% at D=0.26 h-1. This decline in pentose phosphate pathway activity resulted in decreasing molar growth yields on glucose. At dilution rates of 0.05 h-1 and 0.26 h-1 molar growth yields of 19.5 g/mol and 3.2 g/mol, respectively, were obtained. Increase of the steady state glucose concentration in nitrogen-limited chemostat cultures maintained at a constant dilution rate also resulted in a decreased flow of carbon through the pentose phosphate pathway. Above a threshold value of 15–20 mM glucose in the culture, pentose phosphate pathway activity almost completely inhibited. In G. oxydans the coupling between energy generation and growth was very inefficient; yield values obtained at various dilution rates varied between 0.8–3.4 g/cells synthesized per 0.5 mol of oxygen consumed. 相似文献
5.
Reidun Sirevåg 《Archives of microbiology》1975,104(1):105-111
1. Washed cell suspensions of Chlorobium thiosulfatophilum form large amounts of a polyglucose in the light. Addition of acetate to the cells increases the formation of polysaccharide considerably. During incubation in the dark, polysaccharide decreases with time, and organic acids such as succinic and propionic acid are excreted into the medium. 2. Glucose isolated from cells which had photoassimilated 1-, 2-, and U-14C-acetate had a specific activity which lay between 1 and 2 times that of the acetate substrates. 3. To analyse the distribution of radioactivity in the glucose units formed during photoassimilation of 14C-acetate, 2 microbial degradations, with bakers' yeast and Zymomonas mobilis respectively, were used. The results show that acetate gives rise to carbon atoms 1+2 and 5+6 of glucose, whereas carbon atomes 3+4 are not labelled. Further, the results indicate that glucose is not formed via the reductive pentose phosphate cycle when acetate is present. 相似文献
6.
Glucose catabolism by Thiobacillus A2 grown in chemostat culture under carbon or nitrogen limitation
Thiobacillus A2 was grown in glucose- or ammonium-limited chemostats and relative contributions of the Embden-Meyerhof (EM), Entner-Doudoroff (ED) and pentose phosphate (PP) pathways to glucose catabolism estimated by 14C-glucose radiorespirometry. In fast growing strain GFI, the EM pathway predominated (41–79%) under all growth conditions with the PP pathway contributing 18–30%. The ED pathway was apparently absent under some conditions of glucose limitation. In contrast, wild type Thiobacillus A2 exhibited predominance of the EM pathway (43–48%) under ammonium-limitation but apparent predominance of the PP pathway (43–55%) under glucose-limitation, although all three pathways were calculated to operate. Under some conditions of glucose limitation the EM pathway was possibly considerably depressed. No clear pattern of response of the three pathways to altered environmental conditions could be deduced, although marked change in pathway activities were obviously induced. Growth yield was apparently unaffected by variation in pathways. The problems of interpreting such complex radiorespirometric data are discussed.Abbreviations EM
Embden-Meyerhof
- ED
Entner-Doudoroff
- KDPG
2-keto-3-deoxy-6-phosphogluconate
- 6-PG
6-phosphogluconate
- PK
phosphoketolase
- PP
pentose phosphate 相似文献
7.
Phosphon-D (tributyl-2, 4-dichlorobenzylphosphonium chloride), known as an inhibitor of gibberellin biosynthesis, enhances photosynthetic electron transport by up to 200%, with Fe(CN)
6
3-
and NADP+ being the electron acceptors. Maximum stimulation is reached at phosphon-D concentrations around 2–5 M. At the same time photosynthetic ATP formation is gradually inhibited. Phosphon-D concentrations over 0.1 mM inhibit electron transport. The uncoupling activity of phosphon-D is manifested by inhibition of noncyclic ATP synthesis and by stimulation of light-induced electron flow. The inhibition of ATP synthesis drastically decreases photosynthetic carbon assimilation in a reconstituted spinach chloroplast system. The two ATP-dependent kinase reactions of the reductive pentose phosphate cycle become the rate-limiting steps. On the other hand a stimulated photoelectron transport increases the NADPH/NADP+ ratio, resulting in a drastic inhibition of chloroplast glucose-6-phosphate dehydrogenase (EC 1.1.1.49), the key enzyme of the oxidative pentose phosphate cycle. When light-induced electron flow is inhibited by high phosphon-D concentrations and the NADPH/NADP+ ratio is low, the light-dependent inhibition of glucose-6-phosphate dehydrogenase is gradually abolished.Abbreviations AMO-1618
2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidinecarboxylate methyl chloride
- B-Nine
N-dimethylaminosuccinamic acid
- CCC
(2-chloroethyl)-trimethylammonium chloride
- DCMU
3-(3,4-dichlorophenyl)-1, 1-dimethyl urea
- DCPIP
dichlorophenolindophenol
- G-6-PDH
glucose-6-phosphate dehydrogenase
- FBP
fructose bisphosphate
- F-6-P
fructose-6-phosphate
- 3-PGA
3-phosphoglyceric acid
- Posphon-D
tributyl-2,4-dichlorobenzylphosphonium chloride
- PMP
pentose monophosphates
- PPC
pentose phosphate cycle
- RuBP
ribulose bisphosphate
- Ru-5-P
ribulose-5-phosphate
Dedicated to Prof. Dr. Drs.h.c. Adolf Butenandt on the occasion of his 75. birthday 相似文献
8.
Importance of the pentose phosphate pathway for d-glucose catabolism in the obligatory aerobic yeast Rhodotorula gracilis
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d-Glucose catabolism of a phosphofructokinase-deficient yeast Rhodotorula gracilis has been studied. By using d-glucose specifically 14C-labelled at different positions and measuring the distribution of the label in various fractions of cell metabolism, the following results were found. 1. The pentose phosphate pathway, being the main pathway of d-glucose catabolism, simultaneously converts glucose molecules into pentose phosphates oxidatively by using two NADP-linked dehydrogenases and via the non-oxidative transketolase–transaldolase pathway. 2. From the correlation of the 14CO2 liberation and the d-glucose consumption and from the fact that the pentose phosphate moiety in nucleic acids is almost equally labelled from d-[1-14C]- and d-[6-14C]-glucose, it is concluded that of the glucose utilized about 80% undergoes transformation via the non-oxidative pentose phosphate pathway. Only about 20% of glucose is directly decarboxylated to pentose phosphate. 3. For further degradation it is postulated that the pentose phosphates are split into C2 fragments and glyceraldehyde 3-phosphates. 4. All three loci of oxidative decarboxylation appear to be effective in Rh. gracilis, the oxidative part of the pentose phosphate pathway, the decarboxylation of pyruvate in the later part of the glycolytic pathway as well as the oxidation in the tricarboxylic acid cycle. 5. d-Glucose molecules taken up are only partially oxidized to CO2: about four-fifths of each glucose molecule metabolized is incorporated into cell constituents. 6. The quantitative interrelations of the fluxes of d-glucose subunits along the catabolic pathways have been estimated and are discussed. 相似文献
9.
32P was applied to a Laminaria digitata thallus and the pattern of 32P phosphorylated compounds was studied, as a function of time, in the different tissues involved in translocation, i.e. source, pathway and sinks. The results showed that, 3 hours after absorption by the uptake region (lamina), the bulk of the radioactivity was incorporated into organic compounds (70 to 80% of total 32P taken up), hexose monophosphates being the heaviest labelled. Further change in that region was marked by an accumulation of 32P in the inorganic pool (65 to 70% after 13 days). Conversely, the 32P pattern in the medulla of the stipe, which initially showed a similar pattern to the uptake region, did not vary during translocation. The pattern of 32P distribution into sinks (growing stipe peripheral tissue or hapteron) leads to accumulation of the radioactive element in inorganic and acid-insoluble fractions. These results are discussed in terms of comparative distribution of 32P in the different parts of the thallus and suggest that phosphate moves as Pi in that alga.Abbreviations TCA
trichloroacetic acid
- Po
organic phosphate
- Po sol
acid-soluble organic phosphate fraction
- Po insol
acidinsoluble organic phosphate fraction
- Pi
morganic phosphate fraction
- P lip
lipidic phosphate
- Np
protein nitrogen
- ATP
adenosine triphosphate
- ADP
adenosine diphosphate
- PEP
phosphoenolpyruvic acid
- PGA
phosphoglyceric acid
- G-1-P
glucose-1-phosphate
- G-6-P
glucose-6-phosphate
- UDPG
uridine diphosphoglucose 相似文献
10.
Carbon metabolism of chloroplasts in the dark: Oxidative pentose phosphate cycle versus glycolytic pathway 总被引:2,自引:0,他引:2
The conversion of U-labelled [14C]glucose-6-phosphate into other products by a soluble fraction of lysed spinach chloroplasts has been studied. It was found that both an oxidative pentose phosphate cycle and a glycolytic reaction sequence occur in this fraction. The formation of bisphosphates and of triose phosphates was ATP-dependent and occurred mainly via a glycolytic reaction sequence including a phosphofructokinase step. The conversion, of glucose-6-phosphate via the oxidative pentose phosphate cycle stopped with the formation of pentose monophosphates. This was found not to be because of a lack in transaldolase (or transketolase) activity, but because of the high concentration ratios of hexose monophosphate/pentose monophosphate used in our experiments for simulating the conditions in whole chloroplasts in the dark. Some regulatory properties of both the oxidative pentose phosphate cycle and of the glycolytic pathway were studied.Abbreviations DHAP
dihydroxyacetone phosphate
- GAP
3-phosphoglyceraldehyde
- PGA
3-phosphoglycerate
- HMP
hexose monophosphates
- including F6P
fructose-6-phosphate
- G6P
glucose-6-phosphate
- GIP
glucose-1-phosphate
- 6-PGL
phosphogluconate
- PMP
pentose monophosphates
- including R5P
ribose-5-phosphate
- Ru5P
ribulose-5-phosphate
- X5P
xylulose-5-phosphate
- E4P
erythrose-4-phosphate
- S7P
sedoheptulose-7-phosphate
- FBP
fructose-1,6-bisphosphate
- SBP
sedoheptulose-1,7-bisphosphate
- RuBP
ribulose-1,5-bisphosphate 相似文献
11.
Krook J; Vreugdenhil D; Dijkema C; van der Plas L 《Journal of experimental botany》1998,49(329):1917-1924
Cells were grown in batch culture on a mixture of 50 mM glucose and
fructose as the carbon source; either the glucose or the fructose was
[1-13C]-labelled. In order to investigate the uptake
and conversion of glucose and fructose during long-term labelling
experiments in cell suspensions of Daucus carota L.,
samples were taken every 2 d during a 2 week culture period and sucrose and
starch were assayed by means of HPLC and 13C-nuclear
magnetic resonance. The fructose moieties of sucrose had a lower labelling
percentage than the glucose moieties. Oxidative pentose phosphate pathway
activity in the cytosol is suggested to be responsible for this loss of
label of especially C-1 carbons. A combination of oxidative pentose
phosphate pathway activity, a relatively high activity of pathway to
sucrose synthesis and a slow equilibration between glucose-6-phosphate and
fructose-6-phosphate could explain these results. Starch contained glucose
units with a much lower labelling percentage than glucose moieties of
sucrose: it was concluded that a second, plastid-localized, oxidative
pentose phosphate pathway was responsible for removal of C-1 carbons of the
glucosyl units used for synthesis of starch. Redistribution of label from
[1-13C]-hexoses to
[6-13C]-hexoses also occurred: 18-45% of the label
was found at the C-6 carbons. This is a consequence of cycling between
hexose phosphates and those phosphates in the cytosol catalysed by PFP. The
results indicate that independent (oxidative pentose phosphate pathway
mediated) sugar converting cycles exist in the cytosol and
plastid.Key words: Daucus carotaL., cell suspensions,
carbon-13 nuclear magnetic resonance, 13C-NMR,
carbohydrate cycling, oxidative pentose phosphate pathway, plastid.
相似文献
12.
The pentose phosphate pathway in relation to fat synthesis in the developing castor oil seed 总被引:1,自引:0,他引:1
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Slices of 25- to 28-day-old developing castor bean endosperm were incubated with various 14C- and 3H-labeled substrates to determine the amount of glucose dissimilated in the pentose phosphate pathway and to determine the use of the reduced nucleotides so produced in fatty acid synthesis. Ten to 12% of the metabolized glucose traversed the pentose phosphate pathway, and reduced nicotinamide adenine dinucleotide phosphate (NADPH) production would be sufficient to supply 51 to 68% of the reducing equivalents required for fat synthesis. However, using 3H-NADPH produced from 3-3H-glucose as a tracer, it was found that only 40% of the NADPH produced in the pentose phosphate pathway was used in fat synthesis. Thus the actual contribution of the reducing equivalents generated from the pentose phosphate pathway to fat synthesis was 20 to 27% of that required. Because of the methods and assumptions, this value represents a minimal estimate of NADPH used in fat synthesis, and the actual contribution may be somewhat higher. However, tritium from 3H-NADH generated from 1-3H-ethanol was incorporated into fatty acids, and it is contended that NADH may supply a large proportion of the reducing equivalents necessary for fat synthesis in this tissue. 相似文献
13.
1. The carbon isotope discrimination properties of a representative of each of the three types of photosynthetic bacteria Chlorobium thiosulfatophilum, Rhodospirillum rubrum and Chromatium and of the C3-alga Chlamydomonas reinhardii were determined by measuring the ratio of 13CO2 to 12CO2 incorporated during photoautotrophic growth. 2. Chromatium and R. rubrum had isotope selection properties similar to those of C3-plants, whereas Chlorobium was significantly different. 3. The results suggest that Chromatium and R. rubrum assimilate CO2 mainly via ribulose 1,5-diphosphate carboxylase and the associated reactions of the reductive pentose phosphate cycle, whereas Chlorobium utilizes other mechanisms. Such mechanisms would include the ferredoxin-linked carboxylation enzymes and associated reactions of the reductive carboxylic acid cycle.Abbreviations RuDP
ribulose 1,5-disphosphate
- PEP
phosphoenolpyruvate 相似文献
14.
We have used [2-13C]d-glucose and carbon-13 nuclear magnetic resonance (NMR) spectroscopy to investigate metabolic fluxes through the major pathways of glucose metabolism in intact human erythrocytes and to determine the interactions among these pathways under conditions that perturb metabolism. Using the method described, we have been able to measure fluxes through the pentose phosphate pathway, phosphofructokinase, the 2,3-diphosphoglycerate bypass, and phosphoglycerate kinase, as well as glucose uptake, concurrently and in a single experiment. We have measured these fluxes in normal human erythrocytes under the following conditions: (1) fully oxygenated; (2) treated with methylene blue; and (3) deoxygenated. This method makes it possible to monitor various metabolic effects of stresses in normal and pathological states. Not only has 13C-NMR spectroscopy proved to be a useful method for measuring in vivo flux through the pentose phosphate pathway, but it has also provided additional information about the cycling of metabolites through the non-oxidative portion of the pentose phosphate pathway. Our evidence from experiments with [1-13C]-, [2-13C]-, and [3-13C]d-glucoses indicates that there is an observable reverse flux of fructose 6-phosphate through the reactions catalyzed by transketolase and transaldolase, even in the presence of a net flux through the pentose phosphate pathway. 相似文献
15.
Bacillus caldotenax was cultivated in chemostat experiments at 65°C with a chemically defined minimal medium. Glycolysis, tricarboxylic acid cycle, pentose phosphate pathway and the respiratory chain were active as demonstrated by measuring the corresponding enzymes. No enzyme activity of the Entner-Doudoroff pathway could be detected. The specific activities of the citrate cycle enzymes were up to 10 times higher as compared to the enzymes of glycolysis. At dilution rates between 0.3 and 2.2 h-1 none of the main metabolic pathways was regulated. In contrast the isocitrate lyase was regulated (drop of activity with increasing growth rates). As a result of a batch culture with glucose and acetate as carbon sources a regulation model was proposed: glucose, or a metabolite of glucose, represses the isocitrate lyase; in the absence of glucose acetate acts as an inducer.Abbreviations DCIP
dichlorphenol indophenol
- ED
Entner-Doudoroff pathway
- EMP
Emden-Meyerhof-Parnas pathway
- ICL
isocitrate lyase
- PP
pentose phosphate pathway
- TCC
tricarbonic acid cycle 相似文献
16.
Christopher Cannizzaro Bjarke Christensen Jens Nielsen Urs von Stockar 《Metabolic engineering》2004,6(4):263
Carotenoid production by microorganisms, as opposed to chemical synthesis, could fulfill an ever-increasing demand for ‘all natural’ products. The yeast Phaffia rhodozyma has received considerable attention because it produces the red pigment astaxanthin, commonly used as an animal feed supplement. In order to have a better understanding of its metabolism, labeling experiments with [1-13C]glucose were conducted with the wildtype strain (CBS5905 T) and a hyper-producing carotenoid strain (J4-3) in order to determine their metabolic network structure and estimate intracellular fluxes.Amino acid labeling patterns, as determined by GC–MS, were in accordance with a metabolic network consisting of the Embden–Meyerhof–Parnas pathway, the pentose phosphate pathway, and the TCA cycle. Glucose was mainly consumed along the pentose phosphate pathway (65% for wildtype strain), which reflected high NADPH requirements for lipid biosynthesis. Although common to other oleaginous yeast, there was no, or very little, malic enzyme activity for carbon-limited growth. In addition, there was no evidence of phosphoketolase activity. The central carbon metabolism of the mutant strain was similar to that of the wildtype strain, though the relative pentose phosphate flux was lower and the TCA cycle flux in accordance with the biomass yield being lower. 相似文献
17.
Gluconobacter oxydans oxidizes glucose via alternative pathways: one involves the non-phosphorylative, direct oxidation route to gluconic acid and ketogluconic acids, and the second requires an initial phosphorylation and then oxidation via the pentose phosphate pathway enzymes. During growth of G. oxydans in glucose-containing media, the activity of this pathway is strongly influenced by (1) the pH value of the environment and (2) the actual concentration of glucose present in the culture. At pH values below 3.5 the activity of the pentose phosphate pathway was completely inhibited resulting in an increased requirement of the organism for nutrient substances, and a poor cell yield. At pH 5.5 a triphasic growth response was observed when G. oxydans was grown in a defined medium. Above a threshold value of 5–15 mM glucose, oxidation of both glucose and gluconate by the pentose phosphate pathway enzymes was repressed, causing a rapid accumulation of gluconic acid in the culture medium. When growing under these conditions, a low affinity for the oxidation of glucose was found (K
s=13 mM). Below this threshold glucose concentration, pentose phosphate pathway enzymes were synthesized and glucose was actively assimilated via this pathway. It was shown that de novo enzyme synthesis was necessary for increased pentose phosphate pathway activity and that assimilation of gluconate by washed cell suspensions was inhibited by glucose. 相似文献
18.
Summary Plants ofPicea abies (L.) Karst were grown in mycorrhizal association withTelephora terrestris (Pers. ex Fr.) andPisolithus tinctorius (Mich. ex Pers.) Coker and Couch on sphagnum peat in petri dishes or Perspex chambers. After 1 yearT. terrestris had formed prominent rhizomorphs which were characterized by light microscopy and investigated for32P-orthophosphate uptake. The absorbed phosphate was transported to sinks throughout the rhizomorphal system as well as into the plant. The calculated translocation velocity and flux rate in the rhizomorph were in the range of 1–3 cm/h and 0.5–4.0 × 10-10 mol cm-2 s-1, respectively. Label was observed to accumulate in the needles 2–3 days after application. Feeding a non-mycorrhized root with32P-orthophosphate led to an accumulation of label in needles within 1 h, but no radioactivity appeared in the associatedT. terrestris rhizomorphs. The rhizomorphs ofP. tinctorius revealed a higher structural differentiation than those ofT. terrestris. Translocation of labelled phosphorus through rhizomorphs ofP. tinctorius into spruce needles was also demonstrated. 相似文献
19.
N Z Baquer M Cascales B C Teo P McLean 《Biochemical and biophysical research communications》1973,52(1):263-269
Isolated liver cells have been used to assess the relative contribution of the pentose phosphate pathway to glucose metabolism. The incorporation of carbon from specifically labelled glucose into 14CO2 by isolated cells gave values (μg.atoms/g.cells/hr) of: C-1, 7.9; C-6, 1.3; C-U, 3.4. The corresponding figures for liver slices were: C-1, 2.3; C-6, 1.6; C-U, 3.0. The most striking difference was the 3.5-fold increase in the oxidation of C-1 of glucose. Isolated cells retain more than 50% of ATP and have a content of intermediates of the glycolytic pathway closely similar to freeze-clamped liver. The relative importance of the pentose phosphate pathway in isolated liver cells, approximately 16% of glucose catabolised, is consistent with the enzyme profile of liver and the reductive synthetic reactions of the tissue. 相似文献
20.
K. J. Lendzian 《Planta》1978,141(1):105-110
Glucose-6-phosphate dehydrogenase (EC 1.1.1.49) from spinach chloroplasts is strongly affected by interactions between Mg2+, proton, and substrate concentrations. Mg2+ activates the enzyme to different degrees; however, it is not essential for enzyme activity. The Mg2+-dependent activation follows a maximum curve, magnitude and position of the maximum being dependent on pH and NADPH/NADP+ ratios. At a ratio of zero and pH 7.2, maximum activity is observed at 10 mM Mg2+. Increasing the NADPH/NADP+ ratio up to 1.7 (a ratio measured in the stroma during a light period), maximum activity is shifted to much lower Mg2+ concentrations. At pH 8.2 (corresponding to the pH of the stroma in the light) and at a high NADPH/NADP+ ratio, enzyme activity is not affected by the Mg2+ ion. The results are discussed in relation to dark-light-dark regulation of the oxidative pentose phosphate cycle in spinach chloroplasts.Abbreviations DTT
dithiothreitol
- G-6-P
glucose-6-phosphate
- G-6-PDH
glucose-6-phosphate dehydrogenase (EC 1.1.1.49)
- PPC
pentose phosphate cycle 相似文献