scholarly journals The utilization of glucose for the synthesis of milk components in the fed and starved lactating goat in vivo

1980 ◽  
Vol 186 (1) ◽  
pp. 301-308 ◽  
Author(s):  
N Chaiyabutr ◽  
A Faulkner ◽  
M Peaker
Keyword(s):  
Mammary Gland ◽  
Fatty Acid ◽  
Pentose Phosphate Pathway ◽  
Acid Synthesis ◽  
Pentose Phosphate ◽  
Glucose Turnover ◽  
Glucose Carbon ◽  
Lactating Goats ◽  
Total Glucose

1. [U-14C]Glucose and [3-3H]glucose were infused into fed and starved lactating goats in order to study glucose metabolism in the mammary gland. 2. Glucose carbon was oxidized and metabolizet to milk lactose, citrate and triacylglycerol in the lactating goat udder. 3. Recycling of glucose carbon in the lactating animal accounted for 10-20% of the total glucose turnover in the whole animal. Recycling of glucose 6-phosphate in the udder accounted for about 25% of the glucose 6-phosphate metabolized. 4. Flux of glucose 6-phosphate through the pentose phosphate pathway was sufficient to account for 34% of the NADPH required for fatty acid synthesis in the gland in the fed animal. 5. Net metabolism of glucose 6-phosphate via the pentose phosphate pathway accounted for 17.8 and 1.2% of the glucose phosphorylated by the mammary gland in the fed and starved animal respectively. Metabolism of glucose 6-phosphate via the pentose phosphate pathway was sufficient to account for all the CO2 produced from glucose in the fed animal, but only 17% of the CO2 produced from glucose in the starved animal.

The effects of acetate and of pyruvate on the pathways of glucose catabolism in lactating mammary tissue. II. Sheep tissue

1969 ◽  
Vol 36 (3) ◽  
pp. 469-478 ◽  
Author(s):  
R. W. Smith ◽  
R. F. Glascock
Keyword(s):  
Pentose Phosphate Pathway ◽  
Acid Synthesis ◽  
Pentose Phosphate ◽  
Mammary Tissue ◽  
Glucose Catabolism ◽  
Glucose Carbon ◽  
Rat Tissue ◽  
The Relationship ◽  
Stimulation Of

SummaryA study was made of the changes in the rates of oxidation of the C(1), C(2) and C(6) atoms of glucose and in the pathways of glucose catabolism in sheep udder tissue in vitro which occurred when acetate and pyruvate were added.Whereas in rat mammary tissue the rate of oxidation of the C(1) atom of glucose was very much greater than that of the C(6) atom, the ratio of the rates of oxidation of these 2 atoms in sheep tissue was less than 2 when glucose was the only substrate.The addition of acetate resulted in an unequal stimulation of the oxidation of these 2 atoms, with the result that the ratio of their rates of oxidation was about doubled. The rate of oxidation of the C(2) atom was also increased.Acetate also increased the participation of the pentose phosphate pathway in glucose catabolism as measured by the incorporation of the C(1) and C(6) atoms of glucose into fatty acids, lactic acid and glycerol.Pyruvate produced little effect on the rate of oxidation of the C(1) atom but somewhat depressed that of the C(6) atom of glucose. At the same time, it caused a large increase in the participation of the pentose phosphate pathway.These results are discussed with reference to re-cycling of glucose carbon in the pentose phosphate pathway and to the relationship between that pathway and fatty acid synthesis. It is noted that the incorporation of glucose carbon into the 3 intermediates used gave values for the participation of that pathway which were in better agreement than was obtained in rat tissue. It is concluded that triose phosphates are more nearly in equilibrium in sheep than in rat mammary tissue.

FATTY ACID AND GLYCERIDE GLYCEROL SYNTHESIS FROM GLUCOSE DURING HIGH RATES OF GLUCOSE UPTAKE IN THE INTACT RAT

1965 ◽  
Vol 43 (4) ◽  
pp. 437-450 ◽  
Author(s):  
A. S. W. de Freitas ◽  
Florent Depocas
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Glucose Uptake ◽  
Fatty Acid Synthesis ◽  
Acid Synthesis ◽  
Component Fatty Acid ◽  
Rat Tissues ◽  
Total Lipids ◽  
Glucose Carbon ◽  
Total Glucose

The extent of incorporation of glucose carbon into total lipids and component fatty acid, neutral glyceride glycerol, and phosphoglyceride glycerol moieties of carcass, liver, and epididymal tissue has been measured in 20 rats under conditions of constant plasma glucose concentration and specific activity. Rates of fatty acid synthesis from glucose and absolute rates of synthesis have also been estimated. Each rat received 750 mg glucose per hour by continuous infusion. The incorporation of glucose carbon into carcass, liver, and epididymal fat was, respectively, 6.2, 0.75, and 0.06% of the total glucose carbon taken up by the rat tissues. Fifty percent of the C14 found in total lipids of carcass and liver was in the fatty acid fraction. Corresponding glyceride glycerol moieties contained approximately 40% of the total activity. The low level of incorporation of glucose carbon into fatty acids and glyceride glycerol indicates that lipogenesis from glucose can only account for a small proportion of the total glucose taken up by the tissues, even at high rates of glucose uptake. Rates of synthesis from glucose of carcass and liver fatty acids were estimated as 1.5 and 0.11 mmoles fatty acid per tissue per day respectively, with corresponding half-lives of 57 and 7.6 days. Absolute rates of fatty acid synthesis were estimated as 2.6 and 0.55 mmoles fatty acid per day for carcass and liver tissue respectively, with corresponding half-lives of 34 and 4.6 days.

scholarly journals Non-conventional pathways enable pennycress (Thlaspi arvense L.) embryos to achieve high efficiency of oil biosynthesis

2020 ◽  
Vol 71 (10) ◽  
pp. 3037-3051 ◽  
Author(s):  
Enkhtuul Tsogtbaatar ◽  
Jean-Christophe Cocuron ◽  
Ana Paula Alonso
Keyword(s):  
Fatty Acid ◽  
High Efficiency ◽  
Biomass Accumulation ◽  
Acid Synthesis ◽  
Pentose Phosphate ◽  
Aviation Fuel ◽  
Substrate Uptake ◽  
In Planta ◽  
Thlaspi Arvense

Abstract Pennycress (Thlaspi arvense L.) accumulates oil up to 35% of the total seed biomass, and its overall fatty acid composition is suitable for aviation fuel. However, for this plant to become economically viable, its oil production needs to be improved. In vivo culture conditions that resemble the development of pennycress embryos in planta were developed based on the composition of the liquid endosperm. Then, substrate uptake rates and biomass accumulation were measured from cultured pennycress embryos, revealing a biosynthetic efficiency of 93%, which is one of the highest in comparison with other oilseeds to date. Additionally, the ratio of carbon in oil to CO2 indicated that non-conventional pathways are likely to be responsible for such a high carbon conversion efficiency. To identify the reactions enabling this phenomenon, parallel labeling experiments with 13C-labeled substrates were conducted in pennycress embryos. The main findings of these labeling experiments include: (i) the occurrence of the oxidative reactions of the pentose phosphate pathway in the cytosol; (ii) the reversibility of isocitrate dehydrogenase; (iii) the operation of the plastidic NADP-dependent malic enzyme; and (iv) the refixation of CO2 by Rubisco. These reactions are key providers of carbon and reductant for fatty acid synthesis and elongation.

scholarly journals Effects of exogenous glucose on glucose metabolism in the lactating goat in vivo

1983 ◽  
Vol 49 (1) ◽  
pp. 159-165 ◽  
Author(s):  
N. Chaiyabutr ◽  
Anne Faulkner ◽  
M. Peaker
Keyword(s):  
Glucose Metabolism ◽  
Plasma Insulin ◽  
Pentose Phosphate ◽  
Glucose Turnover ◽  
Glucose Load ◽  
Glucose Loading ◽  
Exogenous Glucose ◽  
Lactating Goats ◽  
Glucose Supply

1. Glucose turnover in fed and 48 h-starved lactating goats was determined during a glucose load of 500 μmol/min using a continuous infusion of [U-14C]- and [3-3H]glucose.2. Endogenous rates of irreversible glucose turnover (i.e. total rates of irreversible glucose turnover minus the rate of exogenous glucose supply) were depressed during glucose loading by 14 and 62% in the fed and starved animals respectively.3. Plasma glucose concentrations increased significantly by 57 and 88% in the fed and starved goats respectively. Plasma insulin concentrations increased by 108 and 128% in the fed and starved animals respectively.4. Milk yields increased significantly (41%) in the starved animals during glucose loading, but were unaffected in fed animals.5. In both the fed and 48 h-starved goats, mammary glucose metabolism via glycolysis and the pentose phosphate pathway appeared to be stimulated by glucose loading.

scholarly journals Regulation of glycolysis and fatty acid synthesis from glucose in sheep adipose tissue

1982 ◽  
Vol 206 (3) ◽  
pp. 577-586 ◽  
Author(s):  
James P. Robertson ◽  
Anne Faulkner ◽  
Richard G. Vernon
Keyword(s):  
Tissue Culture ◽  
Adipose Tissue ◽  
Fatty Acid ◽  
Pyruvate Kinase ◽  
Fatty Acid Synthesis ◽  
Pyruvate Dehydrogenase ◽  
Glucose Oxidation ◽  
Acid Synthesis ◽  
Pentose Phosphate ◽  
Glucose Carbon

1. The following were measured in adipose-tissue pieces, obtained from 7–9 month-old sheep, before or after the tissue pieces had been maintained in tissue culture for 24 h: the rates of synthesis from glucose of fatty acids, acylglycerol glycerol, pyruvate and lactate; the rate of glucose oxidation to CO2; the rate of glucose oxidation via the pentose phosphate pathway; the activities of hexokinase, glucose 6-phosphate dehydrogenase, phosphofructokinase, pyruvate kinase, pyruvate dehydrogenase and ATP citrate lyase; the intra- and extra-cellular water content; the concentration of various metabolites and ATP, ADP and AMP. 2. The proportion of glucose carbon converted into the various products in sheep adipose tissue differs markedly from that observed in rat adipose tissue. 3. There was a general increase in the rate of glucose utilization by the adipose-tissue pieces after maintenance in tissue culture; largest changes were seen in the rates of glycolysis and fatty acid synthesis from glucose. These increases are paralleled by an increase in pyruvate kinase activity. There was no change in the activities of the other enzymes as measured, although the net flux through all the enzymes increased. 4. Incubation of fresh adipose-tissue pieces for 2–6h led to an increase in the affinity of pyruvate kinase for phosphoenolpyruvate. 5. The rate of pyruvate production by glycolysis was greater than the activity of pyruvate dehydrogenase of the tissue. 6. The results suggest that both pyruvate kinase and pyruvate dehydrogenase have important roles in restricting the utilization of glucose carbon for fatty acid synthesis in sheep adipose tissue.

Contribution of the pentose phosphate pathway to glucose utilization by preimplantation sheep embryos

1993 ◽  
Vol 5 (3) ◽  
pp. 329 ◽  
Author(s):  
RG Wales ◽  
ZF Du
Keyword(s):  
Pentose Phosphate Pathway ◽  
Blastocyst Stage ◽  
Pentose Phosphate ◽  
Yolk Sac ◽  
Glucose Turnover ◽  
Experimental Conditions ◽  
Advanced Embryo ◽  
Total Glucose ◽  
Total Turnover ◽  
Pentose Pathway

The activity of the pentose phosphate pathway of glucose metabolism in early sheep embryos and in the structures of the advanced conceptus from Day 13 to Day 19 of pregnancy was measured quantitatively during a 2.5-h incubation with glucose as sole energy source. For embryos during cleavage, activity of this pathway accounted for 6-9% of total glucose utilized. The proportion of glucose metabolized through the pentose pathway fell progressively with development and by Day 19 represented 1-2% of glucose turnover. However, total turnover of glucose increased eight fold between the 2-cell and blastocyst stage and the amount of glucose processed through the pentose pathway increased over this time despite the fall in the proportion utilized in this way. In contrast, glucose turnover by the advanced embryo and its extra embryonic membranes progressively decreased as the structures developed. As a result, estimates of the amount of glucose utilized through the pathway per microgram dried weight per hour declined to low values at Day 19 following the peak in activity at about the time of blastulation. Trophoblast and yolk sac processed less glucose through the pentose pathway per microgram dried weight than embryonic tissue but the allantois was similar to the embryo. Overall, the pentose pathway accounted for a relatively constant proportion of the CO2 produced from glucose under these experimental conditions with values generally between 15 and 20% of total CO2 produced. When activities in the components of the advanced conceptus were expressed as the total amount of glucose processed through the pathway per hour, turnover in the embryo, allantois and yolk sac increased progressively with time. By contrast, there was a substantial trough in the activity of the trophoblast on Day 17 of pregnancy.

scholarly journals Pentose cycle and reducing equivalents in rat mammary-gland slices

1972 ◽  
Vol 128 (4) ◽  
pp. 879-899 ◽  
Author(s):  
Joseph Katz ◽  
P. A. Wals
Keyword(s):  
Amino Acids ◽  
Fatty Acids ◽  
Mammary Gland ◽  
Fatty Acid ◽  
Specific Radioactivity ◽  
Acid Synthesis ◽  
Glucose Carbon ◽  
Rat Mammary Gland ◽  
Reducing Equivalents

1. Slices of mammary gland of lactating rats were incubated with glucose labelled uniformly with 14C and in positions 1, 2, 3 and 6, and with 3H in all six positions. Glucose carbon atoms are incorporated into CO2, fatty acids, lipid glycerol, the glucose and galactose moieties of lactose, lactate, soluble amino acids and proteins. C-3 of glucose appears in fatty acids. The incorporation of 3H into fatty acids is greatest from [3-3H]glucose. 3H from [5-3H]glucose appears, apart from in lactose, nearly all in water. 2. The specific radioactivity of the galactose moiety of lactose from [1-14C]- and [6-14C]-glucose was less, and that from [2-14C]- and [3-14C]-glucose more, than that of the glucose moiety. There was no randomization of carbon atoms in the glucose moiety, but it was extensive in galactose. 3. The pentose cycle was calculated from 14C yields in CO2 and fatty acids, and from the degradation of galactose from [2-14C]glucose. A method for the quantitative determination of the contribution of the pentose cycle, from incorporation into fatty acids from [3-14C]glucose, is derived. The rate of the reaction catalysed by hexose 6-phosphate isomerase was calculated from the randomization pattern in galactose. 4. Of the utilized glucose, 10–20% is converted into lactose, 20–30% is metabolized via the pentose cycle and the rest is metabolized via the Embden–Meyerhof pathway. About 10–15% of the triose phosphates and pyruvate is derived via the pentose cycle. 5. The pentose cycle is sufficient to provide 80–100% of the NADPH requirement for fatty acid synthesis. 6. The formation of reducing equivalents in the cytoplasm exceeds that required for reductive biosynthesis. About half of the cytoplasmic reducing equivalents are probably transferred into mitochondria. 7. In the Appendix a concise derivation of the randomization of C-1, C-2 and C-3 as a function of the pentose cycle is described.

Glucose metabolism in the female rat adipocyte: lipid synthesis from glucose during pregnancy and progesterone treatment

1983 ◽  
Vol 97 (2) ◽  
pp. 207-212 ◽  
Author(s):  
M.-Th Sutter-Dub ◽  
A. Sfaxi ◽  
P. Strozza
Keyword(s):  
Fatty Acid ◽  
Glucose Metabolism ◽  
Fatty Acid Synthesis ◽  
Pentose Phosphate Pathway ◽  
Lipid Synthesis ◽  
Acid Synthesis ◽  
Pentose Phosphate ◽  
Ovariectomized Rats ◽  
Female Rat ◽  
Progesterone Treatment

Pregnancy and progesterone treatment of ovariectomized rats decrease glucose metabolism through the pentose-phosphate pathway in isolated female rat adipocytes. As demonstrated in previous studies, progesterone directly decreases [1-14C]glucose oxidation through the pentose-phosphate pathway and lipogenesis from [6-14C]glucose; the present study therefore compared glucose-induced lipid synthesis during pregnancy (10, 16 and 20 days of pregnancy) with the effect of progesterone treatment (5 mg/rat per day for 14 days) to shed more light on the role of this steroid in glucose metabolism during pregnancy. The inhibition of [6-14C]glucose incorporation into triacylglycerols in the progesterone-treated rats was comparable to that which occurs during late (20 days) and mid-pregnancy (16 days) but not during early pregnancy (10 days). The inhibition of fatty acid synthesis was more important as pregnancy advanced and was different from the decrease in fatty acid synthesis induced by progesterone treatment. The sensitivity to insulin was comparable in virgin, ovariectomized and progesterone-treated ovariectomized rats but not in pregnant rats. This implies that progesterone and insulin affect glucose-induced lipid synthesis by distinct processes and that the impaired glucose metabolism is characterized by a reduction in basal glucose utilization rather than by an impaired insulin response.

scholarly journals Evidence for a role of insulin in the regulation of lipogenesis in lactating rat mammary gland. Measurements of lipogenesis in vivo and plasma hormone concentrations in response to starvation and refeeding

1978 ◽  
Vol 176 (1) ◽  
pp. 343-346 ◽  
Author(s):  
A M Robinson ◽  
J R Girard ◽  
D H Williamson
Keyword(s):  
Mammary Gland ◽  
Fatty Acid ◽  
Fatty Acid Synthesis ◽  
Plasma Insulin ◽  
Acid Synthesis ◽  
Plasma Insulin Concentration ◽  
Rat Mammary Gland ◽  
Plasma Hormone

Fatty acid synthesis in the mammary gland of lactating rats in vivo was 5-fold higher than in the liver. Starvation decreased fatty acid synthesis in the gland 50-fold, whereas refeeding for 2h completely reversed this change. The plasma insulin concentration decreased 2-fold in starvation and was restored to the fed-rat value on refeeding. Glucagon and prolactin concentrations did not always change in parallel with lipogenesis, suggesting that insulin may be a regulator of this process in the gland.

Contribution of pentose phosphate pathway in developing castor bean endosperm

1971 ◽  
Vol 49 (2) ◽  
pp. 267-272 ◽  
Author(s):  
P. K. Agrawal ◽  
D. T. Canvin
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Fatty Acid Synthesis ◽  
Pentose Phosphate Pathway ◽  
Castor Bean ◽  
Lipid Synthesis ◽  
Experimental Period ◽  
Acid Synthesis ◽  
Pentose Phosphate ◽  
Fat Synthesis

Glucose-1-14C, glucose-6-14C, and glucose-U-14C were used to calculate the contribution of the PPP in developing castor bean endosperm tissues. Depending on the age of the seed 5–12% of the glucose-14C used was metabolized via the PPP and 88–95% via the EMP pathway. When lipid synthesis was rapid (20- to 28-day period) the PPP contribution was also at a maximum. During the 30- to 51-day period when lipid synthesis decreased so did the PPP contribution.With the data obtained from the PPP contribution the amount of NADPH produced during the experimental period was calculated. Also, the amount of fatty acids synthesized during that period was determined from glucose-U-14C data and thus the amount of NADPH required was calculated. Assuming that all the NADPH produced in the PPP was utilizable in fatty acid synthesis it was found that it was only sufficient to supply 50–75% of the reducing hydrogen required for fat synthesis. Therefore, the rest of the reducing hydrogen must come from some other sources, possibly NADH.

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