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1.
γ-Irradiation of preclimacteric banana resulted in a gradual increase in fructose content, which reached a maximum in 6 days. Although the catabolism of glucose-U-14C was less in irradiated banana, incorporation of label into fructose was high. Initial fructose accumulation in irradiated banana may be due to a shift in glucose utilization from the glycolytic to the pentose phosphate pathway. The ratio of resporatory CO2 from glucose-6-14C and glucose-1-14C was halved in irradiated bananas indicating predominance of the pentose phosphate pathway. The radioactivity of fructose derived from glucose-6-14C was almost twice that from glucose-1-14C in irradiated bananas, whilst in control both fruit the labelled precursors yielded equal amounts. Studies on individual enzymes in these two pathways showed an increase in phosphorylase, phosphoglucomutase, glucose-6-phosphate dehydrogenase and fructose-6-phosphatase and a decrease in hexokinase in irradiated banana.  相似文献   

2.
When specifically labelled glucose was fed to strawberry leaves,the C6/C1, quotient (rate of release of 14CO2 from glucose-6-14C/rateof release of 14CO2 from glucose-114C ranged from 0.27 to 0.35in leaves in water and from 0.46 to 0.96 in leaves fed withiodoacetate. These quotients indicate that both the glycolyticand the pentose phosphate pathways participate in the respirationof strawberry leaves, with a greater contribution from the formerin the iodoacetate increased CO2 output. Concurrently with the increase of CO2 output in iodoacetate,the contents of glucose-6-phosphate (G6P), fructose-6 (F6P)and fructose-1,6-diphosphate (FDP) increased greatly; therewas a smaller increase of phosphoenol-pyruvate (PEP). The increasein the CO2 output in iodoacetate may be explained solely onthe basis that the increases of G6P and FDP accelerate the ratesrespectively of the pentose phosphate pathway and of glycolysisand traffic into the tricarboxylic acid cycle. The increasein content of G6P and FDP is attributed to an increase in theaccessibility of enzymes and substrates caused by iodoacetate.Alternatively the increased CO2 output in iodoacetate may bepartly due to uncoupling of oxidative phosphorylation.  相似文献   

3.
The aim of this work was to establish the pathways of carbohydrate oxidation used in the dark by leaves of Pisum sativum and Triticum aestivum. Segments of young and mature leaves of pea released the carbons of glucose-[14C] as 14CO2 in the order 3,4 > 1 > 2 > 6 whereas in segments of young and mature leaves of wheat the order was 3,4 > 1 > 6 > 2. The detailed labelling of the constituents of mature leaves of wheat by glucose-[1-14C], -[2-14C], -[3,4-14C], and -[6-14C] was determined and showed that the high yield of CO2 from C-6 relative to that from C-2 was due to release of C-6 during pentan synthesis. Estimates were made of the maximum catalytic activities of phosphofructokinase and glucose-6-phosphate dehydrogenase in pea and wheat leaves of three ages. The results of all the above investigations strongly indicate that both pea and wheat leaves in the dark oxidize carbohydrate via glycolysis and the pentose phosphate pathway with the latter accounting for no more than a third of the total. No evidence was obtained of any major change in the relative activities of the two pathways during the development of either type of leaf.  相似文献   

4.
The pathway (s) of glucose degradation in detached senescent and non-senescent tobacco leaves from plants approximately 100 days old were studied utilizing‘Relabeled carbohydrates. Comparable samples of each tissue were allowed to metabolize glucose-1- and glucose-6-14C and C6/C1 ratios were computed from the radioactivity of 14CO2 collected. Two methods of calculation were compared. Hexose monophosphate pathway activity was also compared in both ages of tissue by measuring 14CO2 respired from substrate ribose-1-, xylose-1- and gluconic acid-6-14C. The results indicate that the hexose monophosphate pathway accounts for approximately 25 percent of the respired CO2 in both senescent and non-senescent tissues. Both types of tissue were equally efficient in degrading HMP shunt intermediates to CO2.  相似文献   

5.
J. A. Pryke  T. ap Rees 《Planta》1976,131(3):279-284
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   

6.
R Gilles 《Life sciences》1974,15(7):1363-1369
Isolated axons of Eriocheir sinensis show high ratios of 14CO2 production from glucose-1-14C to 14CO2 production from glucose-6-14C (ratio C1/C6). During osmotic stresses, there is a modification in 14CO production from glucose-6-14C as well as in the ratio C1/C6 while 14CO2 production from glucose-1-14C does not change significantly. These results are interpreted in terms of activity of oxidative and non-oxidative pathways of glucose metabolism.  相似文献   

7.
Two serotype 1 strains ofLegionella pneumophila, Phildelphia 2 and Bellingham, were tested for their ability to metabolize five common substrates by measuring14CO2 released and14C-carbon incorporated into macromolecules. No major differences were noted between the two strains or preparations grown in the yolk sac of chick embryos or agar-broth diphasic medium, following 2 or 14 pasaages on agar. Glutamate was the most actively metabolized substrate, followed by glutamine. Acetate, glucose, and succinate were utilized at much more moderate rates. Changes in cell density and substrate concentration altered the channeling of glutamate and glucose into CO2 and macromolecules. Specific CO2 felease from glutamate was greatest at low cell density and high substrate concentration, while carbon incorporation was increased at high substrate concentration. A reciprocal relationship was noted with glucose: the proportion of carbon incorporation was enhanced at low substrate concentration, but CO2 release paralleled increases in substrate concentration. The pH optimum for glutamate carbon incorporation and CO2 release was 5.5 and 6.1, respectively, but 25% of both activities were retained at pH 3.1. CO2 release from glucose was maximal at pH 7.5 with negligible activity at pH 3.1. Pathways of glucose metabolism were explored by employing glucose, glucose-1-phosphate, and glucose-6-phosphate labeled in various carbon positions. The glycolytic pathway appeared to play a lesser role than the pentose phosphate and/or Entner-Doudoroff pathways. Glucose-1-phosphate was metabolized at a much higher rate than glucose or glucose-6-phosphate. We conclude that glutamate is utilized primarily as an energy source while glucose may serve as an important metabolite for the nutrition ofL. pneumophila.  相似文献   

8.
Abstract— The activities of each enzyme associated with the pentose phosphate pathway as well as the non-enzymatic intermediates in this pathway were measured in synaptosomes isolated from rat cerebral cortex. The specific activities of transketolase (EC 2.2.1.1) and transaldolase (EC 2.2.1.2) were significantly lower in synaptosomes than cerebral cortex; however, the specific activities of glucose-6-phosphate dehydrogenase (EC 1.1.1.49), 6-phosphogluconate dehydrogenase (EC 1.1.1.44), ribosephosphate isomerase (EC 5.3.1.6) and ribulosephosphate epimerase (EC 5.1.3.1.) were comparable in homogenates of synaptosomal fractions and cerebral cortex. Concentrations of most intermediates of the pentose pathway were also similar in extracts of synaptosomes and brain homogenates. Six hours after treatment of rats with the nicotinamide analog, 6-aminonicotinamide (6-AN), 6-phosphogluconate levels in synaptosomes were increased 5-fold; however, glucose-6-phosphate levels remained unchanged. During a 30 min in uitro incubation 6-phosphogluconate levels increased approx 2-fold in synaptosomes obtained from 6-AN treated rats but did not change in synaptosomes from untreated rats. During the same period glucose-6-phosphate levels decreased in synaptosomes from both control and 6-AN treated rats. The conversion of both [1-14C]glucose and [6-14C]glucose to 14CO2 was depressed in synaptosomes from 6-AN treated rats; however, the ratio of the two isotopes converted to 14CO2 was essentially the same. It is concluded that the pentose phosphate pathway is active in nerve endings both in vivo and in vitro.  相似文献   

9.
Changes in activities of the glycolytic and pentose phosphate (PP) pathways in glucose catabolism in various parts of the hypocotyls obtained from 4-day-old etiolatedPhaseolus mungo seedlings were investigated by measuring the inhibition rates of respiration by iodoacetate and malonate, and the release of14CO2 from [1-14C]- and [6-14C]glucose. The relative activity of the PP pathway in glucose catabolism was higher in the immature part (Part I) and the aged part (Part V) of the hypocotyls than in the intermediary one (Part III), while the activity of the glycolytic pathway decreased with aging. On a fresh weight basis, the enzyme activities of the glycolytic and PP pathways were higher in Part I than in Parts III and V. On a protein content basis, however, activities of the enzymes of the PP pathway increased with aging and differentiation of the hypocotyls whereas those of the glycolytic pathway decreased. Levels of nicotinamide adenine nucleotides were found to be in the following order: Part I>Part III> Part V for NAD++NADH; Part I>Part V>Part III for NADP++NADPH. The stimulative effect of methylene blue on decreasing the C6/C1 ratio was greater in Part III than in Part I, and No effect was observed in Part V. These data suggest that a decrease in the activity of the glycolytic pathway with aging and differentiation may be due to the decreasing glycolytic enzyme activities and NAD(H) content. The higher activity of the PP pathway in the immature part is attributable to larger amounts of NADP(H) and enzymes of the PP pathway. The greater contribution of the PP pathway to glucose catabolism in the aged part than in the intermediary part seems to results from a more active turnover of NADP and the relatively higher activity of the enzymes of the PP pathway than those of the glycolytic pathway.  相似文献   

10.
On incubation of the callus tissue ofDaucus carota L. in solutions of glucose-6-14C and -1-14C the distribution of radioactivity in the molecule of endogenous glucose will change and the ratio of activities of liberated14CO2 (C6/C1) will rise The limits of possible changes of specific activity of14CO2 and of the C6/C1 ratio were calculated with respect to the observed randomization and it was shown that the mutual exchange of carbon atoms in the molecules is not the decisive cause of the rise of the ratio. The specific radioactivity of14C in CO2 is as much as 12 times higher than that of endogenous glucose and fructose and about twice as high as the theoretical maximum. This might indicate that in addition to the cytoplasmic fraction of glucose the callus cells contain a fraction of low metabolic activity, most likely in the vacuoles, that could account for some of the increase of the C6/C1 value. The main reason for the changes in the C6/C1 ratio is envisaged in the establishment of isotopic equilibrium between the pentose cycle and glycolysis and other metabolic systems, in particular via triose phosphates, the radioactivity of which can greatly affect the C6/C1 ratio, as was shown in a model experiment.  相似文献   

11.
The metabolism of [1-14C]- and [6-14C]glucose, [1-14]ribose, [1-14C]- and [U-14C]alanine, and [1-14C]- and [5-14C]glutamate by the promastigotes of Leishmania braziliensis panamensis was investigated in cells resuspended in Hanks' balanced salt solution supplemented with ribose, alanine, or glutamate. The ratio of 14CO2 produced from [1-14C]glucose to that from [6-14C]glucose ranged from about two to six, indicating appreciable carbon flow through the pentose phosphate pathway. A functional pentose phosphate pathway was further demonstrated by the production of 14CO2 from [1-14C]ribose although the rate of ribose oxidation was much lower than the rate of glucose oxidation. The rate of 14CO2 production from [1-14C]glucose was almost linear with time of incubation, whereas that of [6-14C]glucose accelerated, consistent with an increasing rate of flux through the Embden-Meyerhof pathway during incubation. Increasing the assay temperature from 26°C to 34°C had no appreciable effect on the rates or time courses of oxidation of either [1-14C]- or [6-14C]glucose or of [1-14C]ribose. Both alanine and glutamate were oxidized by L. b. panamensis, and at rates comparable to or appreciably greater than the rate of oxidation of glucose. The ratios of 14CO2 produced from [1-14C]- to [U-14C]alanine and from [1-14C]- to [5-14C]glutamate indicated that these compounds were metabolized via a functioning tricarboxylic acid cycle and that most of the label that entered the tricarboxylic acid cycle was oxidized to carbon dioxide. Heating the cultures for 6 or 12 h at 34°C, which converts the promastigotes into an ellipsoidally shaped intermediate form, decreased the rates of oxidation of glucose, alanine, and glutamate. The oxidation of glutamate decreased by about 50% and 70% after a 6-h or 12-h heat treatment, respectively. Returning the heated cultures to 26°C initiated a reversion to the promastigote form and recovery of the rate of glucose oxidation, but glutamate oxidation did not return to control levels by 19 h at 26°C.  相似文献   

12.
Summary The metabolism and fate of specifically labeled glucose-14C were compared to mannitol-l-14C and arabitol-l-14C during basidiospore germination of Schizophyllum commune on glucose-asparagine minimal broth. Glucose-l-14C metabolism led to more 14CO2 evolution than glucose-6-14C in spores and the former activity increased upon germination. Liberation of 14CO2 from glucose-3,4-14C increased at 8 h to 12 h of germination and exceeded the amount of radioactive 14CO2 released from glucose-1-14C. The 14CO2 released from glucose-2-14C increased continually during germination while only minor changes in 14CO2 evolution occurred with glucose-6-14C. Unlabeled ethanol (0.25 M) inhibited 14CO2 evolution with glucose-3,4-14C and ungerminated spores and this inhibition disappeared upon germination.More 14CO2 was evolved from labeled glucose during germination and less radioactivity became associated with cellular material. Of the latter, alcohol-soluble extracts of spores or germlings contained mainly radioactive trehalose, less mannitol and little or no labeled arabitol, and this decreased upon germination. Germlings also converted more radioactive glucose-14C into KOH-insoluble material and KOH-soluble components. Spores or germlings converted arabitol-1-14C primarily into trehalose and this was not the case for mannitol-1-14C.  相似文献   

13.
Purified pea root plastids were supplied with glutamine, 2-oxoglutarate and phosphorylated sugars. Formation of glutamate was linear for 75 min and dependent upon the intactness of the organelle. Glucose-6-phosphate and ribose-5-phosphate were the most effective substrates in supporting glutamate synthesis. Flux through the oxidative pentose phosphate pathway during glutamate synthesis in purified plastids was followed by monitoring the release of 14CO2 from [1-14C]glucose-6-phosphate. 14CO2 evolution from C-1 was dependent upon the presence of both glutamine and 2-oxoglutarate and could be inhibited by the application of azaserine. The data are discussed in view of the role of the oxidative pentose phosphate pathway in non-photosynthetic plastids.  相似文献   

14.
The possible role of the pentose phosphate shunt in insulin release was investigated in vitro with collagenase isolated pancreatic islets of rats. Parameters measured were insulin released into the medium and measured by an immunoassay and formation of 14CO2 from glucose labeled either in the C-1 or C-6 position. The in vitro effect of the following substances was studied:
1. 1. 6-Aminonicotinamide, an antimetabolite in the synthesis of pyridine nucleotides. In islets of animals pretreated with 6-amino nicotinamide 6 h previously and in the presence of 3 mg/ml glucose in the incubation medium, 6-aminonicotinamide markedly reduced oxidation of [1-14C]glucose but did not affect that of glucose labeled in C-6. Concomitantly there was a marked decrease in insulin release. This action of 6-aminonicotinamide did not take place when it was added only to the incubation medium. Pretreatment with 6-aminonicotinamide did not change the insulin concentration of the islets, making it unlikely that it interfered with insulin synthesis. The effect of 6-aminonicotinamide is consistent with partial inhibition of the pentose shunt.
2. 2. Methylene blue: this agent was selected because it is known from studies with red blood cells that it will oxidize NADPH and thus stimulate activity of the pentose shunt. In concentrations of 0.5 and 2 μg/ml, methylene blue markedly stimulated oxidation of [1-14C]glucose but not that of C-6. Simultaneously there was a dose related decrease of insulin released.
3. 3. Pyridine nucleotides: in the absence of glucose only NADPH exhibited a significant effect of insulin release. If glucose (3 mg/ml) was present 1 or 10 mM of NAD+ or NADH exhibited a significant effect, NADP+ or NADPH were less effective. If the pentose shunt was blocked by pretreatment with 6-aminonicotinamide, all 4 pyridine nucleotides stimulated insulin release. Similarly there was an increase in oxidation of [1-14C]glucose, consitent with restimulation of the pentose shunt.
4. 4. Nicotinamide by itself exhibited a small effect; however, it was much less than the one produced by equimolar concentrations of the pyridine nucleotides.
Conclusion: Restricted availability of NADPH either less production or by fast removal leads to a decrease in glucose-induced insulin release. Pyridine nucleotides will restimulate 6-aminonicotinamide blockade insulin release and glucose oxidation by the pentose shunt. Recently it has been proposed by others that the polyol pathway may play a key role in insulin release, our data are consistent with such a hypothesis. Furthermore they do support a major role of the pentose shunt in insulin release.  相似文献   

15.
Translocation of Photosynthate in Curly Top Virus-infected Tomatoes   总被引:1,自引:0,他引:1       下载免费PDF全文
Photosynthate translocation in single leaflets of healthy and curly top virus-infected tomatoes was investigated using 14C as a marker. The amount of radioactivity found in plant parts not exposed to 14CO2 was substantially lower in diseased than in healthy plants. The time lag for the appearance of 14C in the petiole was considerably longer in the infected plants than in the healthy. The kinetics of disappearance of 14C from the lamina during the 24-hour period following labeling showed a strong retention of recent assimilates within the diseased leaf, not accompanied by increased immobilization into insoluble forms. Sucrose was the predominant compound participating in photosynthate transport in both healthy and diseased leaves. The amount of 14CO2 fixed was approximately 40% lower in curly top virus-infected leaves than in healthy leaves.  相似文献   

16.
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   

17.
The rate of conversion of glucose-1-14C and glucose-6-14C to 14CO2 and lipid was monitored in queen and worker larvae between 48 and 96 hr of age. A definite dimorphism in glucose metabolism between castes was established. Worker larvae 72 hr of age have a much greater C6C1 ratio than do queen larvae of the same age. The ratios were of the same order of magnitude for both castes of larvae younger or older than 72 hr. Queen larvae were shown to have a greater rate of lipid synthesis than worker larvae.  相似文献   

18.
Many changes that occur in a cell during the cell cycle can be demonstrated in synchronous cultures and can reveal dimensions of cell metabolism not attainable by the study of balanced growth of asynchronous populations in batch cultures or the steady state in chemostat cultures. The release of 14CO2 from specifically labeled glucose by phased (continuously synchronized) cultures follows a characteristic pattern (profile) that depends upon the stage in the cell cycle and the period of labeling used. Successive profiles throughout a cycle showed differences that were altered under different nutrient-limiting growth conditions. Profiles obtained with glucose-1-14C, glucose-2-14C, glucose-3,4-14C, and glucose-6-14C and phased cells of Candida utilis under N-, P-, and C-limited growth demonstrated the variable character of the metabolic activity that occurred in the cells while contour changes within the profiles across the cycle indicated possible correlations with activities of the hexose monophosphate, Embden-Meyerhof-Parnas, and tricarboxylic acid cycle pathways during the cell cycle. The basis of these changes and their use as elementary parameters for study of problems of physiological changes in vivo are considered.  相似文献   

19.
Abstract— The available models of carbohydrate metabolism are not suitable for analysis of experiments on dorsal root ganglia of chicken embryos because they assume that certain products of the pentose cycle mix freely with those of glycolysis, which appears not to be true in this tissue, and because full isotopic equilibration, needed before the start of measurements, is not achieved while the excised ganglia are reasonably fresh. Therefore, new equations were developed which assume only a steady state of relevant metabolic intermediates and make use of the process of isotopic equilibration as a source of information. It is also assumed that an initially unknown but calculable fraction of the products of each pentose cycle re-enters the next cycle, the remainder leaking either to glycolysis or to the incubation medium. From measurements of the time course of output of labelled CO2 in the presence of [1-14C]- and [6-14C]glucose and the incorporation and release in lactate of labelled C from [l-14C]glucose, the equations permit the estimation of many features of carbohydrate metabolism, such as the partitioning of material between the pentose cycle and glycolysis, the partitioning of CO2 output between the pentose and citric acid cycles, the partitioning of the products of glycolysis between CO2 and other destinations, such as lactate, and the degree of recycling from one pentose cycle into the next. In addition, the time course of labelled CO2 output from [2-14C]glucose can be predicted; this, by comparison with the observed output, serves to support some variants of the basic model, while invalidating others. In dorsal root ganglia from 15-day chicken embryos, the assumption of a metabolic steady state was supported by a constant output of labelled CO2 from [l-14C]glucose for 15 or more hours, except for the initial period of isotopic equilibration. By use of the new equations, it is concluded that in these ganglia (a) recycling in the pentose cycle can be 100% efficient in some incubation conditions, but not in others, (b) more CO2 is released from the pentose cycle than from the citric acid cycle, (c) large, quantifiable differences exist between the utilization of the various carbon atoms of glucose, and (d) a pool of intermediates within the pentose cycle, with a time constant of about 1 h, explains a large delay observed in the output of C-6 of glucose into CO2, which occurs with a time constant as long as 5 h under some conditions. Under conditions where recycling is complete in the pentose cycle, this cycle must operate in isolation from glycolysis, which would otherwise convert much of the output of the pentose cycle to lactate. This may explain the role of fructose-1,6-diphospha-tase in the tissue, without recourse to the oft-proposed, puzzling, and ATP-degrading‘futile cycle’between fructose-6-P and fructose-1,6-diP. It is proposed that the new equations may be suitable for similar analyses on some, but not all, other tissues.  相似文献   

20.
1. The C14O2 production by Arbacia eggs and embryos from glucose-1-C14, glucose-2-C14, and glucose-6-C14 has been measured without and with dinitrocresol in the incubation medium. In the absence of the dinitrocresol, the C14O2 production from glucose-1-C14 is more rapid than from glucose-2-C14 and much more rapid than from glucose-6-C14; this, together with previous findings, indicates that glucose is utilized in Arbacia eggs predominantly via the TPN shunt rather than via the aldolase step of the glycolytic pathway. In the presence of the dinitrocresol, C14O2 from glucose-6-C14 approaches that from glucose-1-C14, indicating that, in the presence of this reagent, glucose utilization is diverted from the shunt to the glycolytic pathway. 2. Incorporation of C14 from glucose labelled in the 1-, 2-, or 6- positions into other metabolic products of the eggs and embryos is also inhibited by dinitrocresol, particularly incorporation into the acid-insoluble fraction containing nucleoproteins.  相似文献   

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