The pentose phosphate pathway in rabbit liver. Studies on the metabolic sequence and quantitative role of the pentose phosphate cycle by using a system in situ
- 1 August 1971
- journal article
- Published by Portland Press Ltd. in Biochemical Journal
- Vol. 123 (5), 923-943
- https://doi.org/10.1042/bj1230923
Abstract
1. The reactions of the pentose phosphate cycle were investigated by the intraportal infusion of specifically labelled [(14)C]glucose or [(14)C]ribose into the liver of the anaesthetized rabbit. The sugars were confined in the liver by haemostasis and metabolism was allowed to proceed for periods up to 5min. Metabolism was assessed by measuring the rate of change of the specific radioactivity of CO(2), the carbon atoms of glucose 6-phosphate, fructose 6-phosphate and tissue glucose. 2. The quotient oxidation of [1-(14)C]glucose/oxidation of [6-(14)C]glucose as measured by the incorporation into respiratory CO(2) was greater than 1.0 during most of the time-course and increased to a maximum of 3.1 but was found to decrease markedly upon application of a glucose load. 3. The estimate of the pentose phosphate cycle from C-1/C-2 ratios generally increased during the time-course, whereas the estimate of the pentose phosphate cycle from C-3/C-2 ratios varied depending on whether the ratios were measured in glucose or hexose 6-phosphates. 4. The distribution of (14)C in hexose 6-phosphate after the metabolism of [1-(14)C]ribose showed that 65-95% of the label was in C-1 and was concluded to have been the result of a rapidly acting transketolase exchange reaction. 5. Transaldolase exchange reactions catalysed extensive transfer of (14)C from [2-(14)C]glucose into C-5 of the hexose 6-phosphates during the entire time-course. The high concentration of label in C-4, C-5 and C-6 of the hexose 6-phosphates was not seen in tissue glucose in spite of an unchanging rate of glucose production during the time-course. 6. It is concluded that the reaction sequences catalysed by the pentose phosphate pathway enzymes do not constitute a formal metabolic cycle in intact liver, neither do they allow the definition of a fixed stoicheiometry for the dissimilation of glucose.Keywords
This publication has 40 references indexed in Scilit:
- Effect of insulin and diet on the steady state concentrations of intermediates of the pentose phosphate pathway of glucose metabolism in liverFEBS Letters, 1968
- Enzymes and intermediates of the pentose phosphate pathway in liver and hepatomasBiochimica et Biophysica Acta (BBA) - General Subjects, 1968
- Contribution of the pentose cycle to glucose metabolism in muscleArchives of Biochemistry and Biophysics, 1965
- Pathways of carbohydrate metabolism and their physiological significanceJournal of Chemical Education, 1965
- Anion-exchange chromatography of sugar phosphates with triethylammonium borateJournal of Chromatography A, 1964
- The Croonian Lecture, 1963 GluconeogenesisProceedings of the Royal Society of London. B. Biological Sciences, 1964
- On the response of hepatic glucose-6-phosphate dehydrogenase activity to changes in diet composition and food intake patternAdvances in Enzyme Regulation, 1963
- Differential degradation of d- and l-glycerol-1-C14 by Aerobacter aerogenesArchives of Biochemistry and Biophysics, 1958
- Pathways of Glycogen Formation in Liver and Skeletal Muscle in Fed and Fasted Rats1JCI Insight, 1957
- Xylulose-5-phosphate, a new intermediate in the pentose phosphate cycleArchives of Biochemistry and Biophysics, 1955