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1.
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   

2.
Glucose metabolism of healthy and tobacco mosaic virus-infected leaf-discs of Nicotiana tabocum L. var. Xanthi showing local-necrotic lesions was investigated using glucose-14C. Local lesion formation following inoculation with tobacco mosaic virus resulted in enhanced glucose metabolism reflected by an increased rate of release of 14CO2 from glucose-U-14C and greater incorporation of 14C into all cell fractions. When specifically labelled glucose was fed to healthy and tobacco mosaic virus infected leaves, the C6/C1 ratio (rate of release of 14CO2 from glucose-6-14C/rate of release of 14CO2 from glucose-l-14C) was similar for healthy and virus-infected leaves. The C6/C1 ratios recorded from 0.30 to 0.50 indicate that both the glycolytic and pentose phosphate pathways participate in glucose catobolism in healthy and virus-infected leaves. Although the C6/C1 ratio was the same as that of the healthy leaf the rate of release of 14CO2 from glucose-6-14C and glucose-1-14C was greatly increased in the virus-infected leaf. The increased glucose catabolism occurs by both glycolytic and pentose phosphate pathways in the virus-infected leaf.  相似文献   

3.
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   

4.
With 14CO2, d-glucose-[U-14C] and dl-mevalonate-[4R-4-3H1] used as precursors, a study was made of the labelling dynamics of the steryl glucosides (SG) and steryl acylglucosides (ASG) in Sinapis alba seedlings. The radioactivity of the sterol and sugar moieties, as well as of the fatty acid moieties in the case of ASG, was analysed separately. The course of incorporation of 14C from 14 CO2 and glucose-[U-14C] into the sugar part of SG and ASG indicated that about 23 of the whole pool of the newly synthesized sterol glycosides of both types underwent rapid deglucosylation. Likewise, fatty acids in the ASG pool were rapidly exchanged. The present results point to a high metabolic activity of the sterol glycoside derivatives in plant cells.  相似文献   

5.
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   

6.
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   

7.
A doubly labeled 3-ketoceramide, [1-14C] lignoceroyl [1-3H2] 3-ketosphingosine (3H14C ratio, 3.61) was injected into the left ventricle of rat heart. The ceramide isolated from the livers of the animals after 1 hr incubation contained an equal 3H>14C ratio of 3.60. This finding strongly supports the existence for direct conversion of 3-ketoceramide to ceramide in rat liver.  相似文献   

8.
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   

9.
10.
In vivo biosynthesis of -linolenic acid in plants   总被引:6,自引:0,他引:6  
[1-14C]acetate was readily incorporated into unsaturated fatty acids by leaf slices of spinach, barley and whole cells of Chlorellapyrenoidosa and Candidabogoriensis. In these systems the [14C] label in newly synthesized oleate and linoleate was approximately equally distributed in the C1–9 and the C10–18 fragments obtained by reductive ozonolysis of these acids, whereas in a-linolenic acid over 90% of the total [14C] was localized in the C1–9 fragment. While [1-14C]oleic acid was converted by whole cells of Chlorella to [1-14C]linoleic and [1-14C]linolenic acids, [U-14C]oleic acid yielded [U-14C]linoleic acid but a-linolenic acid was labeled only in the carboxyl terminal carbon atoms. When spinach leaf slices were supplied with carboxyl labeled octanoic, decanoic, dodecanoic, tetradecanoic and octadecanoic acids, only the first three acids were converted to a-linolenic acids while the last two acids were ineffective. Thus we suggest that (a) linoleic acid is not the precursor of a-linolenic acid and (b) 12:3(3, 6, 9) is the earliest permissible trienoic acid which is then elongated to a-linolenic acid.  相似文献   

11.
12.
Commercial [5-14C]mevalonate is shown to contain several radioactive impurities, which give artifactually high amounts of Hyamine bound, volatile acidic radioactivity when incubated with killed or living rat renal cortex slices, as compared with [5-14C]mevalonate purified either by liquid-liquid partition chromatography or through the enzymically generated R-5-phospho-[5-14C]mevalonate by ion-exchange chromatography. The artifactual 14CO2 results were not diluted by incubation with increasing amounts of unlabelled mevalonate, whereas the 14CO2 and [14C]cholesterol produced by rat renal cortex slices incubated with purified [5-14C]mevalonate were both diluted to the same extent by unlabelled mevalonate. It is concluded that R[5-14C]mevalonate is genuinely oxidized to 14CO2invitro, and that purification of substrate before its use is necessary. Production of 14CO2 and various [14C]lipids from purified [5-14C]mevalonate, as a function of time and substrate concentration, by renal cortex and liver slices, is described.  相似文献   

13.
Sun-Shine Yuan 《Steroids》1982,39(3):279-289
A-ring enollactones 1a, 1b or 9 derived from 4-cholesten-3-one, testosterone benzoate or 3-oxo-4-estren-17β-yl benzoate were condensed with [1,2-13C2]acetyl chloride to give intermediates 2a, 2b or 10. 2a and 2b were cyclized by acid or base to give 3,4-13C2-labeled 4-cholesten-3-one and testosterone, respectively. [3,4-13C2]4-Cholesten-3-one was converted via reduction of its trimethylsilyl enol ether to [3,4-13C2]cholesterol. Acetyl enollactone 10 was cyclized in acetic acid to [3,4-13C2]3-oxo-4-estren-17β-yl benzoate followed by aromatization and hydrolysis to produce [3,4-13C2]estradiol-17β. Alternatively, cyclization of 10 with base afforded [3,4-13C2]3-oxo-4-estren-17β-ol directly, which was then oxidized and aromatized to yield [3,4-13C2]estrone. Ozonolysis of progesterone, conversion to the diketal ester 16 and acylation followed by acid hydrolysis furnished [3,4-13C2]progesterone.  相似文献   

14.
Dichloroacetate (2 mm) stimulated the conversion of [1-14C]lactate to glucose in hepatocytes from fed rats. In hepatocytes from rats starved for 24 h, where the mitochondrial NADHNAD+ ratio is elevated, dichloroacetate inhibited the conversion of [1-14C]lactate to glucose. Dichloroacetate stimulated 14CO2 production from [1-14C]lactate in both cases. It also completely activated pyruvate dehydrogenase and increased flux through the enzyme. The addition of β-hydroxybutyrate, which elevates the intramitochondrial NADHNAD+ ratio, changed the metabolism of [1-14C]lactate in hepatocytes from fed rats to a pattern similar to that seen in hepatocytes from starved rats. Thus, the effect of dichloroacetate on labeled glucose synthesis from lactate appears to depend on the mitochondrial oxidation-reduction state of the hepatocytes. Glucagon (10 nm) stimulated labeled glucose synthesis from lactate or alanine in hepatocytes from both fed and starved rats and in the absence or presence of dichloroacetate. The hormone had no effect on pyruvate dehydrogenase activity whether or not the enzyme had been activated by dichloroacetate. Thus, it appears that pyruvate dehydrogenase is not involved in the hormonal regulation of gluconeogenesis. Glucagon inhibited the incorporation of 10 mm [1-14C]pyruvate into glucose in hepatocytes from starved rats. This inhibition has been attributed to an inhibition of pyruvate dehydrogenase by the hormone (Zahlten et al., 1973, Proc. Nat. Acad. Sci. USA70, 3213–3218). However, dichloroacetate did not prevent the inhibition of glucose synthesis. Nor did glucagon alter the activity of pyruvate dehydrogenase in homogenates of cells that had been incubated with 10 mm pyruvate in the absence or presence of dichloroacetate. Thus, the inhibition by glucagon of pyruvate gluconeogenesis does not appear to be due to an inhibition of pyruvate dehydrogenase.  相似文献   

15.
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   

16.
Biosynthesis of N-methyl-l-glucosamine moiety of streptomycin from d-glucose by Streptomyces griseus was studied. A mixture of d-[1-14C]glucose and d-[6-3H]glucose was given to the culture of S. griseus. The 3H/14C ratio found in N-methyl-d-glucosamine further supports a mechanism that the conversion of d-glucose to l-hexose is carried out without scission of carbon skeleton. When d-[1-14C]glucose and d-[3-3H]glucose were used, the fall of 3H/14C ratio in N-methyl-l-glucosamine showed that the hydrogen atom at C-3 plays a rôle in such a transformation.  相似文献   

17.
The activities of alternative pathways of glucose metabolism in developing rat brain were evaluated by measurement of the yields of 14CO2 from glucose labeled with 14C on carbons 1, 2, 3 + 4, 6 and uniformly labeled glucose, from the detritiation of [2-3H]glucose and from the incorporation of 14C from specifically labeled glucose into lipids by brain slices from cerebral hemispheres and cerebellum. The glycolytic route and tricarboxylic acid cycle (14CO2 yield from carbons 3, 4, and 6 of glucose) increased during development. The flux through the glutamate-γ-aminobutyric route (14CO2 yield from carbon 2-carbon 6 of glucose) also showed an increase with development. In contrast, the proportion of glucose metabolized via the pentose phosphate pathway was markedly decreased as development progressed. The artificial electron acceptor, phenazine methosulfate, was used as a probe to investigate the effect of alterations in the redox state of NADP+NADPH couple on a number of NADP-linked systems in developing brain. Phenazine methosulfate produced a massive (20- to 50-fold) stimulation of the pentose phosphate pathway, in contrast, the incorporation of glucose carbon into fatty acids and flux through the glutamate-γ-aminobutyrate shunt were sharply decreased. The effects of phenazine methosulfate on the incorporation of glucose into glyceride glycerol, on the flux of glucose through the pyruvate dehydrogenase reaction and tricarboxylic acid cycle, all processes linked to the NAD+NADH couple, appeared to be minimal in the brain at the stages of development studied, i.e., 1, 5, 10, 20 days, and in the adult rat. The significance of the massive reserve potential of the pentose phosphate pathway in the developing brain is discussed.  相似文献   

18.
We have examined the effects of glucagon on lipogenesis from fasted-refed rats incubated under two conditions, either without added substrate or with 10 mml-lactate. Net glycolysis (from glycogen) occurs in the absence of glucagon. This glycolysis is inhibited by glucagon under conditions of no added lactate, and reversed by glucagon to a net gluconeogenesis in the presence of 10 mm lactate. Glucagon markedly inhibits fatty acid synthesis (estimated by incorporation of tritium from THO) in hepatocytes incubated without added substrate; but, in the presence of 10 mml-lactate, the inhibition of fatty acid synthesis is only about 10%. The inhibition of lipogenesis from endogenous glycogen is primarily caused by inhibition of glycolysis. Glucagon markedly lowers the C-4,5,6C-1,2,3 ratio in glucose produced from [1-14C]galactose, indicating a strong inhibition of phosphofructokinase flux. The C-1,2,3C-4,5,6 ratio in glucose from [1-14C]glycerol is only slightly less than 1, indicating an active fructose diphosphatase flux even under conditions of active net glycolysis. Glucagon increases this ratio only slightly, suggesting that an acute increase of fructose diphosphatase activity by glucagon may occur, but is of much less importance than the decrease of phosphofructokinase.  相似文献   

19.
A-Side (4-R)-(4-2H)-reduced nicotinamide adenine dinucleotide (NADD) was prepared by a stepwise oxidation of ethanol-d6 to acetate in the presence of NAD, alcohol dehydrogenase, and aldehyde dehydrogenase. The B-side (4-S) isomer of NADD was prepared using the glucose dehydrogenase activity of glucose-6-phosphate dehydrogenase to oxidize to oxidize glucose-1-d in 40% dimethyl aulfoxide. Subsequent purifieation of the reduced nucleotides was achieved using a column of strongly basic polystyrene macroporous resin (AG MP-1) eluted with 0.2 m LiCl, pH 10, and applying the pooled NADD peak to a polyacrylamide gel (Bio-Gel P-2) column. The final A260A340 ratio obtained for these preparations was below 2.3. Preparation of the deuterated reduced nucleotides in this manner allows production of specifieally deuterated substrates by coupled enzymatic synthesis. L-Malate-2-d was prepared by coupled synthesis of A-side NADD to the reduction of oxaloacetate by the A-side enzyme malate dehydrogenase.  相似文献   

20.
Isolated livers from fed rats were perfused with a medium containing glucose labeled uniformly with 14C and specifically with 3H. There was considerable formation of glucose from endogenous sources but simultaneously uptake of about half of the 14C in glucose. After 2 hours the 3H14C ratios in perfusate glucose decreased by 55–60% with (2-3H, U-14C), 40–50% with (5-3H, U-14C), 25–30% with (3-3H or 4-3H, U-14C) and by 10–15% with (6-3H, U-14C) glucose. Qualitatively comparable patterns were obtained with rat hepatocytes. These results demonstrate recycling of carbon between glucose and pyruvate. Superimposed upon this there is an extensive futile cycle between glucose and glucose 6-P. There is also futile cycling between fructose 6-P and fructose 1,6 P2 and to a small extent between phosphoenol pyruvate and pyruvate.  相似文献   

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