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1.
The presence of the glycolytic enzymes from hexokinase to pyruvate kinase in plastids of seedling pea (Pisum sativum L.) roots was investigated. The recoveries, latencies and specific activities of each enzyme in different fractions was compared with those of organelle marker enzymes. Tryptic-digestion experiments were performed on each enzyme to determine whether activities were bound within membranes. The results indicate that hexokinase (EC 2.7.1.2) and phosphoglyceromutase (EC 5.4.2.1) are absent from pea root plastids. The possible function of the remaining enzymes is considered.Abbreviations GADPH
glyceraldehyde 3-phosphate dehydrogenase
- PFK
phosphofructokinase
- PFP
pyrophosphate: fructose 6-phosphate 1-phosphotransferase
Bronwen A. Trimming gratefully acknowledges the award of a studentship from the Science and Engineering Research Council 相似文献
2.
When a buffered, aerobic suspension of ethanol-grown cells of Saccharomyces cerevisiae is treated with ethanol, a rapid flux of metabolism is observed from endogenous phosphoenolpyruvate to hexose monophosphates. Intracellular concentrations of phosphoenolpyruvate, 2-phosphoglycerate, and 3-phosphoglycerate record a monotonic drop, while those of triose phosphates and fructose 1,6-diphosphate fall after an early rise; fructose 6-phosphate, mannose 6-phosphate, and glucose 6-phosphate levels rise to a plateau. Prior growth on glucose extinguishes fructose 1,6-diphosphatase activity and completely arrests the rise of the hexose monophosphates. By using mutants blocked at a number of glycolytic steps it has been concluded that the metabolic flow takes place along the Embden-Meyerhof pathway in the reverse direction bypassing pyruvate kinase and fructose 6-phosphate kinase. Ethanol acts as a trigger by supplying NADH at the glyceraldehyde 3-phosphate dehydrogenase step. The rate of the reversal in the span phosphoenolpyruvate to fructose 1,6-diphosphate approaches 40 μ mol of 3-carbon units per minute per gram of wet cells. The in vivo activity of fructose 1,6-diphosphatase is nearly a quarter of this rate. 相似文献
3.
alpha-Glycerophosphate dehydrogenase (EC 1.1.99.5) in mitochondria from liver of the triiodothyronine-treated rats is competitively inhibited by phosphoenolpyruvate, glyceraldehyde 3-phosphate and 3-phosphoglycerate, the apparent Ki values for phosphoenolpyruvate being 0.76 mM at pH 7.0, 1.7 mM at pH 7.4 and 3.5 mM at pH 7.7. The apparent Ki values for glyceraldehyde 3-phosphate and 3-phosphoglycerate are also pH-dependent. Other glycolytic intermediates, such as 2-phosphoglycerate, 2,3-diphosphoglycerate, pyruvate, glucose 6-phosphate, fructose 6-phosphate and fructose 1,6-diphosphate did not alter significantly alpha-glycerophosphate dehydrogenase activity. Palmitoyl-CoA is a competitive inhibitor of this enzyme, with Ki value of about 30 micron. 相似文献
4.
W.B. LeFlore 《Experimental parasitology》1978,46(1):83-91
Cercariae of Plagiorchis elegans Rudolphi 1802 collected from experimentally infected snails, Lymnaea palustris, were subjected to various histochemical tests for dehydrogenase systems. A high degree of activity was demonstrated for succinic dehydrogenase (EC 1.3.99.1), malic dehydrogenase (EC 1.1.1.37), isocitric dehydrogenase (EC 1.1.1.41), α-glycerophosphate dehydrogenase (EC 1.1.1.8), and glucose 6-phosphate dehydrogenase (EC 1.1.1.49). These enzymes were present in the tegument, tail, caudal pocket, excretory bladder, acetabulum, and oral sucker, particularly in the muscles around the stylet. Only moderate activity was obtained for lactic dehydrogenase (EC 1.1.1.27) and 6-phosphogluconate dehydrogenase (EC 1.1.1.44) at these sites, glutamic dehydrogenase (EC 1.4.1.2) was localized only in the tails of the cercariae and tests for alcohol dehydrogenase (EC 1.1.1.1) were completely negative. The cerebral ganglia and its commissures stained intensely in the tests for succinic, isocitric, α-glycerophosphate, and glucose 6-phosphate dehydrogenase systems. The results indicate the possibility that several energy-producing sequences may be available to these cercariae. 相似文献
5.
Adult pairs of Schistosoma mansoni convert glucose to lactate rapidly and almost quantitatively under aerobic and anaerobic conditions E. Bueding, 1950, Journal of General Physiology33, 475–495). Glycolysis is the principal source of energy of schistosomes and its inhibition by trivalent organic antimonials, at the phosphofructokinase step [EC 2.7.1.11], may be the basis for the chemotherapeutic effects of these agents E. Bueding and J. M. Mansour, 1957, British Journal of Pharmacology and Chemotherapy12, 159–165). We have developed standardized conditions for the comparison of rates of glucose consumption and lactate production by intact schistosomes in vitro and by centrifuged homogenates of worms. The rates of glycolysis of homogenates prepared from freshly isolated worms, and from worms that have been lyophilized immediately after harvesting and stored for prolonged periods at ?80 C were identical, when measured in media containing appropriate concentrations of glucose, NAD, ATP, MgCl2, KCl, and phosphate. The specific activities of the 11 glycolytic enzymes and of 3 related enzymes (fructose-biphosphatase [EC 3.1.3.11], glycerol-3-phosphate dehydrogenase [EC 1.1.1.8], and malate dehydrogenase [EC 1.1.1.37]) were measured in homogenates under optimal conditions. The profile of the relative activities of glycolytic enzymes of S. mansoni resembles closely that of Ehrlich ascites tumor cells, and differs markedly from that observed in erythrocytes or skeletal muscle. As is the case in many animal tissues, hexokinase [EC 2.7.1.1] was the enzyme of lowest specific activity, and the rate of glycolysis of homogenates was almost the same as the hexokinase activity. Several other lines of evidence support the view that the hexokinase reaction is the rate-limiting step in the glycolysis of worm homogenates. Hexokinase activity was not particulate in schistosome homogenates, and there was no detectable high Km glucokinase-like activity. The rate of glycolysis by homogenates exceeded that of intact worms by a factor of nearly 5. The contributions of glucose transport, availability of ADP and inorganic phosphate, regulatory enzymes, and a substrate cycle catalyzed by fructose-bisphosphatase are considered as possible mechanisms for the restraint of glycolysis in intact worms. The mechanisms contributing to the rapid rates of glycolysis of adult S. mansoni have not been identified, although several can be excluded (unusually high capacity of the glycolytic enzymes, the presence of mitochondrial hexokinase, the occurrence of glycosomes, and the operation of defective mitochondrial shuttles). In view of the regulatory role of hexokinase in the glycolysis of S. mansoni, inhibition of this enzyme is a potentially important target for the development of new antischistosomal drugs. 相似文献
6.
M. Kaloyianni-Dimitriades Isidoros Beis 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1984,155(1):109-115
Summary
Rana ridibunda erythrocytes have a complete sequence of glycolytic enzymes but not the tricarboxylic acid cycle enzymes.The steady state contents of the glycolytic intermediates were measured in quick frozenRana ridibunda erythrocytes. A comparison of the mass action ratios with the equilibrium constants for the glycolytic reactions showed that phosphoglucomutase, phosphoglucose isomerase, aldolase, triosephosphate isomerase, phosphoglycerate mutase and enolase reactions are all near equilibrium whilst hexokinase, phosphofructokinase and pyruvate kinase are displaced from equilibrium.The steady state contents of glycolytic intermediates, lactate, adenine nucleotides, inorganic phosphate have been measured during various periods up to 4 h of incubation of erythrocytes in the presence of glucose. In the incubation experiment glycolysis had been stimulated by the high pH-value of the medium. After 4 h of incubation 3 patterns of changes can be distinguished. One group of intermediates (glucose, glucose 6-phosphate, 2-phosphoglycerate and inorganic phosphate) in which the concentration of metabolites was lower than the zero time values. A second group of metabolites (fructose 6-phosphate, fructose 1,6-bisphosphate, phosphoenolpyruvate and AMP) in which the concentration was about the same at zero time and after 4 h of incubation. The metabolites of the third group (dihydroxyacetone phosphate, glyceraldehyde 3-phosphate, 1,3-diphosphoglycerate, 2,3-diphosphoglycerate, 3-phosphoglycerate, pyruvate, lactate, ADP, ATP and glucose 1-phosphate) all increased their content during the 4 h of incubation in comparison to the zero time values.From the results it appears that in the amphibian erythrocyte glycolysis seems to be similar to that of mammalian erythrocytes as far its control and organisation is concerned down to the level of PEP, with the exception of the low concentration of phosphoglycerate compounds.Abbreviations
2,3DPG
2,3-diphosphoglycerate
-
EDTA
[ethylene dinitrilo]-tetra-acetic acid
-
P
i
inorganic phosphate
-
DTNB
5,5-dithio-bis-(2-nitrobenzoic acid)
-
PEP
phosphoenolpyruvate
-
RBC
red blood cells 相似文献
7.
Glucose metabolism in the mucosa of the small intestine. Glycolysis in subcellular preparations from the cat and rat 总被引:11,自引:10,他引:1
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1. Lactic acid formation in supernatant fractions of homogenates of cat or rat small-intestinal mucosa was measured under optimum conditions with glucose, fructose, glucose 6-phosphate, fructose 1,6-diphosphate or 3-phosphoglycerate as substrate. 2. Between 80 and 107% of the glycolytic activity of the homogenate was recovered in these particle-free preparations when glucose, fructose, glucose 6-phosphate or fructose 1,6-diphosphate was used as substrate. 3. Evidence was obtained that hexokinase and phosphofructokinase were the rate-limiting enzymes in the initial sequence of glycolytic reactions. The limitation of rate by hexokinase was much more pronounced in preparations from the cat than in those from the rat. 4. With subcellular preparations from cat or rat small intestine lactic acid was also formed from ribose 5-phosphate and at rates similar to those observed with glucose. 5. A higher rate of glycolysis was observed with glucose 6-phosphate as substrate with preparations from the proximal half of the small intestine of the rat as compared with the distal half. 6. Mucosal preparations from rats starved for 24-48hr. exhibited only about one-quarter of the glycolytic activity of those of fed control groups. The decreased rate of formation of lactic acid from either glucose or fructose was mainly due to a decrease in the activity of hexokinase(s). The activities of glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase and a number of other enzymes were not significantly decreased by starvation. 7. The results are discussed in relation to metabolic control of glycolysis in other mammalian tissues. 相似文献
8.
Synthesis and degradation of fructose 2,6-bisphosphate in endosperm of castor bean seedlings 总被引:10,自引:10,他引:0
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The aim of this work was to examine the possibility that fructose 2,6-bisphosphate (Fru-2,6-P2) plays a role in the regulation of gluconeogenesis from fat. Fru-2,6-P2 is known to inhibit cytoplasmic fructose 1,6-bisphosphatase and stimulate pyrophosphate:fructose 6-phosphate phosphotransferase from the endosperm of seedlings of castor bean (Ricinus communis). Fru-2,6-P2 was present throughout the seven-day period in amounts from 30 to 200 picomoles per endosperm. Inhibition of gluconeogenesis by anoxia or treatment with 3-mercaptopicolinic acid doubled the amount of Fru-2,6-P2 in detached endosperm. The maximum activities of fructose 6-phosphate,2-kinase and fructose 2,6-bisphosphatase (enzymes that synthesize and degrade Fru-2,6-P2, respectively) were sufficient to account for the highest observed rates of Fru-2,6-P2 metabolism. Fructose 6-phosphate,2-kinase exhibited sigmoid kinetics with respect to fructose 6-phosphate. These kinetics became hyperbolic in the presence of inorganic phosphate, which also relieved a strong inhibition of the enzyme by 3-phosphoglycerate. Fructose 2,6-bisphosphatase was inhibited by both phosphate and fructose 6-phosphate, the products of the reaction. The properties of the two enzymes suggest that in vivo the amounts of fructose-6-phosphate, 3-phosphoglycerate, and phosphate could each contribute to the control of Fru-2,6-P2 level. Variation in the level of Fru-2,6-P2 in response to changes in the levels of these metabolites is considered to be important in regulating flux between fructose 1,6-bisphosphate and fructose 6-phosphate during germination. 相似文献
9.
Metabolic regulation during early frog development: glycogenic flux in Xenopus oocytes, eggs, and embryos 总被引:2,自引:0,他引:2
32P-labeled glucose 6-phosphate and phosphoenolpyruvate were injected into oocytes, fertilized eggs, and early embryos of Xenopus laevis, and the 32P label was followed into glycolytic enzymes and acid-soluble metabolites. The kinetics of labeling of phosphoglucomutase and phosphoglyceromutase and the formation of specific metabolites were used to measure carbon flux through glycolytic intermediates in these cells. In full-grown stage VI oocytes, fertilized eggs, and cells of cleaving embryos, carbon metabolism is in the glycogenic direction. Glycolytic intermediates injected into these cells were metabolized into UDP-glucose and then presumably into glycogen. Carbon flow between phosphoenolpyruvate and glucose 6-phosphate does not utilize fructose 1,6-bisphosphatase; rather, it may depend largely on enzymes of the pentose phosphate pathway. Maturation and fertilization of the oocyte did not result in a change in the qualitative pattern of metabolites formed. Pyruvate kinase, although abundant in oocytes and embryos, is essentially inactive in these cells. Pyruvate kinase also appears to be inactive in small previtellogenic stage II oocytes; however, in these cells injected glycolytic intermediates were not metabolized to UDP-glucose. 相似文献
10.
Trypanosoma evansi, which causes surra, is descended from
Trypanosoma brucei brucei, which causes nagana. Although both
parasites are presumed to be metabolically similar, insufficient knowledge of
T. evansi precludes a full comparison. Herein, we provide the
first report on the subcellular localisation of the glycolytic enzymes in T.
evansi, which is a alike to that of the bloodstream form (BSF) of
T. b. brucei: (i) fructose-bisphosphate aldolase,
glyceraldehyde-3-phosphate dehydrogenase (GAPDH), hexokinase, phosphofructokinase,
glucose-6-phosphate isomerase, phosphoglycerate kinase, triosephosphate isomerase
(glycolytic enzymes) and glycerol-3-phosphate dehydrogenase (a glycolysis-auxiliary
enzyme) in glycosomes, (ii) enolase, phosphoglycerate mutase, pyruvate kinase
(glycolytic enzymes) and a GAPDH isoenzyme in the cytosol, (iii) malate dehydrogenase
in cytosol and (iv) glucose-6-phosphate dehydrogenase in both glycosomes and the
cytosol. Specific enzymatic activities also suggest that T. evansi
is alike to the BSF of T. b. brucei in glycolytic flux, which is
much faster than the pentose phosphate pathway flux, and in the involvement of
cytosolic GAPDH in the NAD+/NADH balance. These similarities were expected
based on the close phylogenetic relationship of both parasites. 相似文献
11.
A partially purified preparation of α-glucan phosphorylase was obtained from chloroplasts of Pisum sativum by ion-exchange chromatography and gel filtration. The preparation, in which no other enzyme that metabolized starch or glucose 1 -phosphate could be detected, was characterized. The optimum for phosphorolysis was pH 7.2; at pH 8.0 the activity was reduced by 50%. The preparation showed normal hyperbolic kinetics with the substrates, and catalysed the formation of [14C]glucose 1-phosphate from 14C-labelled starch grains from pea chloroplasts. None of the following, generally at 5 and 10 mM, significantly altered the rate of phosphorolysis: glucose, fructose, sucrose, fructose 6-phosphate, fructose 1,6-bisphosphate, dihydroxyacetone phosphate, 3-phosphoglycerate, 2-phosphoglycerate, phosphoenolpyruvate, pyruvate, ATP, ADP, AMP, 6-phosphogluconate, 2-phosphoglycollate, Mg2+, dithiothreitol. However, phosphorolysis was inhibited by ADPglucose. Measurements of ADPglucose in leaves and in isolated chloroplasts showed that none could be detected in the dark and suggested that the concentration in the light was high enough to cause a modest inhibition of the phosphorylase. The control of the breakdown of chloroplast starch is discussed. 相似文献
12.
Sau-Gee Yung Marvin Paule Russell Beggs Elaine Greenberg Jack Preiss 《Archives of microbiology》1984,138(1):1-8
Enterobacter hafniae and Aeromonas hydrophila ADPglucose synthetases were purified approximately 39-and 61-fold, respectively, over the crude extract. Both enzymes were heat stable at 60°C in the presence of inorganic phosphate. The molecular weights of both enzymes were approximately 200,000 which are similar to other enteric ADPglucose synthetases studied. Based on kinetic results obtained from the partially purified enzymes, the E. hafniae enzyme is activated twofold by phospho-enolpyruvate while the A. hydrophila enzyme is activated twofold by fructose 6-P and 1.5-fold by fructose 1,6 bis-phosphate. The E. hafniae enzyme activity is strongly inhibited by AMP and ADP and the inhibition can be partially reversed by P-enolpyruvate. ADP is the most effective inhibitor of the A. hydrophila enzyme and its inhibiton can be partially overcome by the presence of the activators fructose 6-P and fructose 1,6-P2. These kinetic results show that the allosteric properties of the E. hafniae enzyme are distinctly different from the ADPglucose synthetases of those previously studied from bacteria of the genus Enterobacter. Although the A. hydrophila enzyme is activated by fructose 1,6-P2, its allosteric properties are quite different than those observed for ADPglucose synthetase of the Enterobacteriaceae.Abbreviations Hepes
N-2-hydroxyethylpiperazine-N-2-ethane-sulfonic acid
- glucose 1-P
glucose 1-phosphate
- Bicine
N,N-bis(2 hydroxyethyl)glycine
- fructose 6-P
fructose 6-phosphate
- Mes
2(N-morpholino)-ethane sulfonic acid
- fructose 1,6-P2
fructose 1,6 bis-phosphate
- DTE
dithioerythritol; pyridoxal-P, pyridoxal-phosphate
- fructose 1-P
fructose 1-phosphate
- P-enolpyruvate
phospho-enolpyruvate
- 1,6 hexanediol bis-P
1,6 hexanediol bis-phosphate; glucose 6-P, glucose 6-phosphate
- dihydroxyacetone-P
dihydroxyacetone phosphate
- 1-glycerol-3-P
1-glycerol-3-phosphate
- erythrose 4-P
erythrose 4-phosphate
- 2-P-glycerate
2-phosphoglycerate
- sedoheptulose 1,7-P2
sedoheptulose 1,7 bis-phosphate
- 3-P-glycerate
3-phosphoglycerate
- mannose-6-P
mannose-6-phosphate 相似文献
13.
1. This work was done to compare the amounts of glycolytic intermediates in the club of the spadix of Arum maculatum L. at an early stage (α) of development, immediately prior to the increase in glycolysis (pre-thermogenesis), and at the peak of the rapid glycolysis (thermogenesis).2. Glucose 1-phosphate, glucose 6-phosphate, fructose 6-phosphate, 3-phosphoglycerate, 2-phosphoglycerate, phosphoenolpyruvate and pyruvate were measured. The results indicate that at all the above stages of club development the reactions catalysed by phosphoglucomutase, glucosephosphate isomerase, phosphoglycerate mutase and enolase were close to equilibrium, but those catalysed by phosphofructo-kinase and pyruvate kinase were considerably displaced from equilibrium.3. The amounts of the above compounds per club increased 5-fold between α stage and pre-thermogenesis but the relative amounts remained unchanged. When glycolysis increased by more than 50-fold at thermogenesis, the amount of fructose 1,6-diphosphate per club rose, but no changes were detected in the amounts per club of any of the other compounds listed above. These results are discussed in relation to the control of glycolysis. 相似文献
14.
Glucosephosphate isomerase (EC 5.3.1.9) of Schistosoma mansoni is inhibited competitively by a number of tetrose, pentose, and hexose phosphates with inhibitor constant (Ki) values in the range of 0.5 to 400 μM. The most potent inhibitor is 5-phospho-d-arabinonate which resembles the cis-enediolate transition state intermediate of the reaction. These analogs were also found to be effective inhibitors of the production of lactate from glucose by suitably supplemented worm homogenates. The rank order of potency of inhibition of glycolysis was inversely related to the magnitudes of the Ki values for glucosephosphate isomerase. These Ki values were similar to those previously reported for mammalian glucosephosphate isomerase, suggesting similarities in the steric and electronic characteristics of the active sites of these isofunctional enzymes. This conclusion was further supported by the observed pH dependence of the inhibition by 5-phospho-d-arabinonate. Although glucosephosphate isomerase is not a rate-limiting enzyme of glycolysis, in the conventional sense, its selective inhibition could be of chemotherapeutic importance, in part because of the accumulation in glycolyzing systems of glucose 6-phosphate which is a potent feedback inhibitor of hexokinase. 相似文献
15.
The analogue of fructose 1,6-bisphosphate in which the phosphate group, -O-PO3H2, on C-6 is replaced by the phosphonomethyl group, -CH2-PO3H2, was made enzymically from the corresponding analogue of 3-phosphoglycerate. It was a substrate for aldolase, which was used to form it, but not for fructose 1,6-bisphosphatase. It was hydrolysed chemically to yield the corresponding analogue of fructose 6-phosphate [i.e. 6-deoxy-6-(phosphonomethyl)-D-fructose, or, more strictly, 6,7-dideoxy-7-phosphono-D-arabino-2-heptulose]. This proved to be a substrate for the sequential actions of glucose 6-phosphate isomerase, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase. Thus seven out of the nine enzymes of the glycolytic and pentose phosphate pathways so far tested catalyse the reactions of the phosphonomethyl isosteres of their substrates. 相似文献
16.
The glucose and fructose degradation pathways were analyzed in the halophilic archaeon Halococcus saccharolyticus by 13C-NMR labeling studies in growing cultures, comparative enzyme measurements and cell suspension experiments. H. saccharolyticus grown on complex media containing glucose or fructose specifically 13C-labeled at C1 and C3, formed acetate and small amounts of lactate. The 13C-labeling patterns, analyzed by 1H- and 13C-NMR, indicated that glucose was degraded via an Entner-Doudoroff (ED) type pathway (100%), whereas fructose was degraded almost completely via an Embden-Meyerhof (EM) type pathway (96%) and only to a small extent (4%) via an ED pathway. Glucose-grown and fructose-grown cells contained all the enzyme activities of the modified versions of the ED and EM pathways recently proposed for halophilic archaea. Glucose-grown cells showed increased activities of the ED enzymes gluconate dehydratase and 2-keto-3-deoxy-gluconate kinase, whereas fructose-grown cells contained higher activities of the key enzymes of a modified EM pathway, ketohexokinase and fructose-1-phosphate kinase. During growth of H. saccharolyticus on media containing both glucose and fructose, diauxic growth kinetics were observed. After complete consumption of glucose, fructose was degraded after a lag phase, in which fructose-1-phosphate kinase activity increased. Suspensions of glucose-grown cells consumed initially only glucose rather than fructose, those of fructose-grown cells degraded fructose rather than glucose. Upon longer incubation times, glucose- and fructose-grown cells also metabolized the alternate hexoses. The data indicate that, in the archaeon H. saccharolyticus, the isomeric hexoses glucose and fructose are degraded via inducible, functionally separated glycolytic pathways: glucose via a modified ED pathway, and fructose via a modified EM pathway.Abbreviations. KDG
2-Keto-3-deoxygluconate
- KDPG
2-Keto-3-deoxy-6-phosphogluconate
- FBP
Fructose-1,6-bisphosphate
- TIM
Triosephosphate isomerase
- GAP
Glyceraldehyde-3-phosphate
- PEP
Phosphoenolpyruvate
- PTS
Phosphotransferase
- 1-PFK
Fructose 1-phosphate kinase
An erratum to this article can be found at 相似文献
17.
《Comparative biochemistry and physiology. A, Comparative physiology》1979,62(4):789-796
- 1.1. The activities of all the eight enzymes of conversion of fructose to glucose, of all the three key enzymes of glycolysis and of the two dehydrogenases of pentose shunt were determined in proximal and distal mucosa of small intestine.
- 2.2. With the exception of hexokinase, all of these enzymes have an activity significantly higher in the proximal than distal mucosa.
- 3.3. The gradient along the intestine is particularly important for the three enzymes which are typical for fructose metabolism (ketohexokinase, triokinase and fructose-1-phosphate aldolase), for glucose-6-phosphatase and for phosphofructokinase.
- 4.4. The effects of fructose diet on the enzyme activities are compatible with the results, described in other papers, concerning the final products of metabolism.
- 5.5. The increase of fructose metabolism appears to result mainly from the stimulation of the activities of ketohexokinase and fructose-1-phosphate aldolase which control all the pathways of ketohexose utilization.
- 6.6. The activation of glucose-6-phosphatase, in comparison with the other enzymes which are involved in glucose-6-phosphate metabolism, explains the appearance of the ability to synthesize glucose with fructose as substrate. This enzyme is the only key enzyme of fructose to glucose conversion which responds to fructose feeding in distal mucosa.
- 7.7. The activities of hexokinase and phosphofructokinase are not increased by fructose feeding.
- 8.8. The activity of pyruvate kinase. the only key glycolytic enzyme which is necessarily implicated when fructose is the substrate, is stimulated but less than the typical enzymes of fructose metabolism.
- 9.9. But, because of its quantitative importance, the glycolytic pathway is responsible for the most part of the observed increase of fructose utilization.
- 10.10. The responses of pyruvate kinase, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities to fructose feeding are similar in the two parts of small intestine.
- 11.11. The activities of ketohexokinase, triokinase and glucose-6-phosphate isomerase are stimulated only in the proximal small intestine mucosa.
- 12.12. The other enzyme activities which are stimulated in proximal segment are also increased in distal segment.
- 13.13. All segments of small bowel show adaptive changes to dietary manipulation but not necessarily for all their functions.
- 14.14. The gradient of enzyme activities from the proximal to the distal small intestine persists despite dietary modification, but the data do not determine that this gradient is intrinsic or that it is not intrinsic.
18.
Fluoride-Induced Inhibition of Starch Biosynthesis in Developing Potato, Solanum tuberosum L., Tubers Is Associated with Pyrophosphate Accumulation 总被引:1,自引:1,他引:0
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Pretreatment of discs excised from developing tubers of potato (Solanum tuberosum L.) with 10 millimolar sodium fluoride induced a transient increase in 3-phosphoglycerate content. This was followed by increases in triose-phosphate, fructose 1,6-bisphosphate and hexose-phosphate (glucose 6-phosphate + fructose 6-phosphate + glucose 1-phosphate). The effect of fluoride is attributed to an inhibition of glycolysis and a stimulation of triose-phosphate recycling (the latter confirmed by the pattern of 13C-labeling [NMR] in sucrose when tissue was supplied with [2-13C]glucose). Fluoride inhibited the incorporation of [U-14C] glucose, [U-14C]sucrose, [U-14C]glucose 1-phosphate, and [U-14C] glycerol into starch. The incorporation of [U-14C]ADPglucose was unaffected. Inhibition of starch biosynthesis was accompanied by an almost proportional increase in the incorporation of 14C into sucrose. The inhibition of starch synthesis was accompanied by a 10-fold increase in tissue pyrophosphate (PPi) content. Although the subcellular localization of PPi was not determined, a hypothesis is presented that argues that the PPi accumulates in the amyloplast due to inhibition of alkaline inorganic pyrophosphatase by fluoride ions. 相似文献
19.
When ) growing on glucose was starved for isoleucine by the addition of valine, the intracellular levels of fructose 6-phosphate, fructose 1,6-bisphosphate and dihydroxyacetone phosphate were abruptly decreased to one-half, but those of glucose 6-phosphate and ATP remained constant. In contrast, this was not the case with CP79(). Chloramphenicol released the response observed in CP78. These results suggest that the glycolytic activity is also under the stringent control. Since only glucosephosphate isomerase[EC 5.3.1.9] was significantly inhibited by guanosine 5′-diphosphate 3′-diphosphate among several glycolytic enzymes tested, the enzyme might be responsible for the decrease observed in CP78. 相似文献
20.
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