Enzymic Flux Rates in vivo through the Embden-Meyerhof Pathway and the Nucleotides of the Mouse Liver
| Autor: | J. Günther, J. G. Reich, D. Zahn, H. Frunder, U. Till, M. Tschisgale |
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| Rok vydání: | 1968 |
| Předmět: |
Time Factors
Phosphofructokinase-1 Glucuronates Models Biological Biochemistry Oxidative Phosphorylation Mice chemistry.chemical_compound Adenosine Triphosphate Glycerol Animals Glycolysis Hexosephosphates Pyruvates Glycogen Nucleotides Phosphotransferases Gluconeogenesis Glucose-6-Phosphate Isomerase Phosphorus Isotopes Fructose Fructose-Bisphosphatase Kinetics Glucose Liver chemistry Computers Analog Glycerophosphates Phosphoenolpyruvate carboxykinase Flux (metabolism) Mathematics Phosphofructokinase |
| Zdroj: | European Journal of Biochemistry. 6:384-394 |
| ISSN: | 1432-1033 0014-2956 |
| DOI: | 10.1111/j.1432-1033.1968.tb00459.x |
| Popis: | The enzymic flux rates through the Embden-Meyerhof pathway and the nucleotides of the liver have been measured in vivo with the [32P]Pi-tracer technique. The specific radioactivities of 15 positions in 11 metabolites have been measured within the first minute after injection of carrier-free [32P]Pi. The results have been treated with the analogue computer technique. The main conclusions are: 1 The turnover of all liver compounds examined is in the range of from seconds to minutes. The velocity of oxidative phosphorylation is so high that within 30 sec after the tracer injection prestationary kinetics is observed, indicating that the turnover of the γ-P position of ATP amounts to more than 25 μmoles per g fresh liver per min. 2 The labelling of ATP-γ-P is rapidly redistributed within the other nucleotide β- and γ-P-positions, the reactions of the nucleoside diphosphokinase type being more rapid than with the monophosphokinase type. 3 The rate of net glycolysis or gluconeogenesis is less than 0.1 μmoles per g per min in the postabsorptive state. Synthesis of glycogen or UDP-glucuronic acid via UDPG is less than 0.3 μmoles per g per min. The absolute turnover rate of glucose 6-phosphate is about 3 μmoles per g per min. The pathway of glucose 6-phosphate formation and the fate of glucose 6-phosphate cannot be measured on the basis of 32P-experiments alone. 4 Phosphofructokinase as well as aldolase and fructose 1,6-biphosphate phosphohydrolase are inhibited in vivo. In the latter two cases, adequate kinetic explanation of this phenomenon is not available from in vitro results of the literature. The isotope flux via glucosephosphate isomerase amounts to 0.4 μmoles per g per min. This is about one order of magnitude smaller than expected from the maximal activity and from the kinetic behaviour of the enzyme in vitro. 5 Synthesis of about 0.7 μmoles of glycerol 3-phosphate from ATP and glycerol takes place per g per min. At least 0.7 μmoles of phosphoenolpyruvate are synthesized per g per min without being converted to fructose 1,6-biphosphate. The fate of phosphoenolpyruvate is unknown. Reconversion to pyruvate or conversion to lipid glycerol is possible. |
| Databáze: | OpenAIRE |
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