A putative pathway of glyconeogenesis in skeletal muscle

1981 ◽  
Vol 1 (2) ◽  
pp. 157-165 ◽  
Author(s):  
Bhanu R. Odedra ◽  
T. Norman Palmer
Keyword(s):  
Skeletal Muscle ◽  
Malic Enzyme ◽  
Pyruvate Carboxylase ◽  
Phosphoenolpyruvate Carboxykinase ◽  
De Novo ◽  
Glycogen Biosynthesis ◽  
Glycogen Sparing ◽  
Specific Inhibitors

Evidence is presented in support of a pathway in skeletal muscle of glyconeogenesis (glycogen biosynthesis de novo) from L-glutamate and related amino acids involving the enzyme phosphoenolpyruvate carboxykinase (PEP CK). In the rat hemidiaphragm in vitro, not only did L-[U-14C]glutamate exert a glycogen-sparing action, but14C-label was incorporated into glycogen. The incorporation is thought not to be simply via label randomization and was decreased by factors that increased glycolysis or pyruvate oxidation. 3-Mercaptopicolinate and amino-oxyacetate, specific inhibitors of PEP CK and aminotransferase-type enzymes, respectively, decreased14C-incorporation from L-[U-14C]glutamate into glycogen. No quantitative determination of apparent glyconeogenic flux was made, and it remains to be established whether glyconeogenesis via PEP CK and/or via PEP CK coupled with 'malic' enzyme (or pyruvate carboxylase) is functionally important in skeletal muscle.

Regulation by Phosphoenolpyruvate of Fructose-1,6-diphosphatase in Skeletal Muscle: Evidence for an Allosteric Activator of the Enzyme

1972 ◽  
Vol 50 (6) ◽  
pp. 710-713 ◽  
Author(s):  
Hans W. Behrisch
Keyword(s):  
Skeletal Muscle ◽  
Low Temperature ◽  
High Temperatures ◽  
Pyruvate Carboxylase ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Cold Water ◽  
Gluconeogenic Enzymes ◽  
Allosteric Inhibitor ◽  
Crustacean Muscle ◽  
Allosteric Activator

Fructose-1,6-diphosphatase (FDPase) from muscle of three cold-water crustaceans was found to be activated by phosphoenolpyruvate (PEP). PEP appears to reduce Km for FDP at low and high temperatures; however, at low temperature the effect on Km of FDP is amplified. In addition PEP reduces affinity of FDPase for AMP, the allosteric inhibitor of the enzyme. These results suggest a coupling of several of the regulatory steps in the glycolytic and gluconeogenic sequences. In addition, skeletal muscle of the crustaceans used in the present study contains substantial (higher than 500 μmol/h/g tissue) activities of the gluconeogenic enzymes phosphoenolpyruvate carboxykinase, pyruvate carboxylase, and glucose-6-phosphatase. On the basis of these results it is proposed that gluconeogenesis is a functioning pathway in crustacean muscle.

scholarly journals [14C]bicarbonate fixation into glucose and other metabolites in the liver of the starved rat under halothane anaesthesia. Metabolic channelling of mitochondrial oxaloacetate

1985 ◽  
Vol 227 (3) ◽  
pp. 851-865 ◽  
Author(s):  
D F Heath ◽  
J G Rose
Keyword(s):  
Pyruvate Carboxylase ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Co2 Exchange ◽  
Published Data ◽  
Citrate Cycle ◽  
Incomplete Mixing ◽  
Metabolic Channelling ◽  
Glucose Output

Previous attempts to account for the labelling in vivo of liver metabolites associated with the citrate cycle and gluconeogenesis have foundered because proper allowance was not made for the heterogeneity of the liver. In the basal state (anaesthetized after 24h starvation) this heterogeneity is minimal, and we show that labelling by [14C]bicarbonate can be interpreted unambiguously. [14C]Bicarbonate was infused to an isotopic steady state, and measurements were made of specific radioactivities of blood bicarbonate, alanine, glycerol and lactate, of liver alanine and lactate, and of individual carbon atoms in blood glucose and liver aspartate, citrate and malate. (Existing methods for several of these measurements were extensively modified.) The results were combined with published rates of gluconeogenesis, uptake of gluconeogenic precursors by the liver, and citrate-cycle flux, all measured under similar conditions, and with estimates of other rates made from published data. To interpret the results, three ancillary measurements were made: the rate of CO2 exchange by phosphoenolpyruvate carboxykinase (PEPCK; EC 4.1.1.32) under conditions that simulated those in vivo; the 14C isotope effect in the pyruvate carboxylase (EC 6.4.1.1) reaction (14C/12C = 0.992 +/- 0.008; S.E.M., n = 8); the ratio of labelling by [2-14C]- to that by [1-14C]-pyruvate of liver glutamate 1.5 min after injection. This ratio, 3.38, is a measure of the disequilibrium in the mitochondria between malate and oxaloacetate. The data were analysed with due regard to experimental variance, uncertainties in values of fluxes measured in vitro, hepatic heterogeneity and renal glucose output. The following conclusions were reached. The results could not be explained if CO2 fixation was confined to pyruvate carboxylase and there was only one, well-mixed, pool of oxaloacetate in the mitochondria. Addition of the other carboxylation reactions, those of PEPCK, isocitrate dehydrogenase (EC 1.1.1.42) and malic enzyme (EC 1.1.1.40), was not enough. Incomplete mixing of mitochondrial oxaloacetate had to be assumed, i.e. that there was metabolic channelling of oxaloacetate formed from pyruvate towards gluconeogenesis. There was some evidence that malate exchange across the mitochondrial membrane might also be channelled, with incomplete mixing with that in the citrate cycle. Calculated rates of exchange of CO2 by PEPCK were in agreement with those measured in vitro, with little or no activation by Fe2+ ions.(ABSTRACT TRUNCATED AT 400 WORDS)

Spectrophotometric determination of de novo hemozoin/β-hematin formation in an in vitro assay

2004 ◽  
Vol 325 (1) ◽  
pp. 85-91 ◽  
Author(s):  
Abhai K Tripathi ◽  
Shabana I Khan ◽  
Larry A Walker ◽  
Babu L Tekwani
Keyword(s):  
Spectrophotometric Determination ◽  
De Novo ◽  
In Vitro Assay ◽  
Vitro Assay

Respiration and carbohydrate energy metabolism of the lung-dwelling parasite Rhabdias bufonis (Nematoda: Rhabdiasoidea)

Parasitology ◽  
1978 ◽  
Vol 76 (1) ◽  
pp. 21-27 ◽  
Author(s):  
A. O. Anya ◽  
G. M. Umezurike
Keyword(s):  
Lactate Dehydrogenase ◽  
Energy Metabolism ◽  
Malate Dehydrogenase ◽  
Malic Enzyme ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Weight Basis ◽  
Fresh Weight ◽  
Fresh Weight Basis ◽  
Alternative Pathways

SummaryAn investigation of the carbohydrate energy metabolism of Rhabdias bufonis, the lung-dwelling nematode parasite of the African toad, Bufo regularis, indicates that the nematode stores very little glycogen (0·137 ± 0·003% on a fresh weight basis) but does utilize oxygen in vitro. The intracellular distribution and high levels of activity observed for the enzymes phosphoenolpyruvate carboxykinase, pyruvate kinase, lactate dehydrogenase, malate dehydrogenase, malic enzyme and fumarate reductase suggest two alternative pathways of carbohydrate energy metabolism.

The enigmatic presence of all gluconeogenic enzymes in Schistosoma mansoni adults

Parasitology ◽  
1991 ◽  
Vol 102 (2) ◽  
pp. 267-276 ◽  
Author(s):  
A. G. M. Tielens ◽  
P. Van Der Meer ◽  
J. M. Van Den Heuvel ◽  
S. G. Van Den Bergh
Keyword(s):  
Skeletal Muscle ◽  
Schistosoma Mansoni ◽  
Rat Liver ◽  
Pyruvate Carboxylase ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Rat Skeletal Muscle ◽  
Gluconeogenic Enzymes ◽  
Muscle Tissues ◽  
Order Of Magnitude ◽  
C Nmr

SUMMARYThe activities of glucose-6-phosphatase (G6Pase), frucrose-1,6-bisphosphatase (FBPase), phosphoenolpyruvate carboxykinase (PEPCK) and pyruvate carboxylase (PC) were determined in homogenates of adult Schistosoma mansoni worms and compared with the activities in homogenates of rat liver and rat skeletal muscle, tissues with a high and a low gluconeogenic capacity, respectively. All four gluconeogenic enzymes were present in S. mansoni. The enzymes were less active than in rat liver, but the activities of G6Pase, PEPCK and PC were at least an order of magnitude higher than in rat skeletal muscle whereas FBPase was approximately equally active in S. mansoni and in rat muscle. Experiments with 14C-labelled substrates or [14C]NaHCO3 failed to demonstrate the actual occurrence of gluconeogenesis in S. mansoni. Some possible other functions of the gluconeogenic enzymes were investigated. Experiments with inhibitors of PEPCK gave no indications that this enzyme was involved in the degradation of glucose. This was confirmed by 13C-NMR experiments which indicated that lactate was formed from phosphoenolpyruvate via the actions of pyruvate kinase and lactate dehydrogenase, and that PEPCK did not participate in the formation of lactate. Substrate cycling between fructose-6-phosphate and fructose-1,6-bisphosphate was demonstrated to occur in adult S. mansoni. This shows that FBPase participates in the glucose metabolism of this parasite.

Skeletal muscle glycogen phosphorylase akinetics: effects of adenine nucleotides and caffeine

2001 ◽  
Vol 91 (5) ◽  
pp. 2071-2078 ◽  
Author(s):  
James W. E. Rush ◽  
Lawrence L. Spriet
Keyword(s):  
Skeletal Muscle ◽  
Muscle Glycogen ◽  
Glycogen Phosphorylase ◽  
Adenine Nucleotides ◽  
Dependent Manner ◽  
Skeletal Muscle Glycogen ◽  
Sparing Effect ◽  
Dose Dependent ◽  
Glycogen Sparing

This study aimed to determine physiologically relevant kinetic and allosteric effects of Pi, AMP, ADP, and caffeine on isolated skeletal muscle glycogen phosphorylase a (Phos a). In the absence of effectors, Phos a had V max = 221 ± 2 U/mg and K m = 5.6 ± 0.3 mM Pi at 30°C. AMP and ADP each increased Phos a V max and decreased K m in a dose-dependent manner. AMP was more effective than ADP (e.g., 1 μM AMP vs. ADP: V max = 354 ± 2 vs. 209 ± 8 U/mg, and K m = 2.3 ± 0.1 vs. 4.1 ± 0.3 mM). Both nucleotides were relatively more effective at lower Pi levels. Experiments simulating a range of contraction (exercise) conditions in which Pi, AMP, and ADP were used at appropriate physiological concentrations demonstrated that each agent singly and in combination influences Phos a activity. Caffeine (50–100 μM) inhibited Phos a( K m ∼8–14 mM, ∼40–50% reduction in activity at 2–10 mM Pi). The present in vitro data support a possible contribution of substrate (Pi) and allosteric effects to Phos a regulation in many physiological states, independent of covalent modulation of the percentage of total Phos in the Phos a form and suggest that caffeine inhibition of Phos a activity may contribute to the glycogen-sparing effect of caffeine.

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