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Carbohydrate and carbohydrate metabolite utilization by enzyme systems of mouse brain and liver mitochondria

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Abstract

1. Both mouse brain and mouse liver preparations were found to utilize substrates characteristic of the following carbohydrate enzyme systems : the glycogen, glucose, fructose, mannose, fructose-1-phosphate (5), oxidative pentose phosphate (4), and tricarboxylic acid system. 2. Each of these enzyme systems was found on isolated brain mitochondria and a number on isolated liver mitochondria. 3. The implications of these findings in regard to the lability, normal enzyme system complement and functions of mitochondria are discussed.

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... Although it is generally agreed that brain mitochondria, like mitochondria from other tissues, carry out citric acid cycle oxidations and oxidative phosphorylation, there are varying reports in the literature concerning the relationship of the enzymes of glycolysis to the mitochondrial fraction of brain. Hesselbach and Du Buy (1,2) showed that brain mitochondria convert glucose and glycolytic intermediates to lactate both aerobically and anaerobically. Similarly, Gallagher et al. (3) demonstrated the complete oxidation of glucose and glucose-6-phosphate to carbon dioxide and water by brain mitochondria. ...
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A mitochondrial fraction prepared from calf brain cortex possessed negligible glycolytic activity in the absence of the enzymes of the high speed supernatant fraction. When mitochondria were added to a supernatant system supplemented with optimal amounts of crystalline hexokinase, a 20 per cent stimulation of glycolysis was observed. The supernatant fraction produced minimal amounts of lactate in the absence of exogenous hexokinase; the addition of mitochondria doubled the lactate production. The substitution of glycolytic intermediates for glucose as substrates as well as the addition of exogenous glycolytic enzymes to the supernatant fraction or supernatant fraction plus mitochondria indicated that the mitochondria contributed mainly hexokinase and phosphofructokinase. By direct assay of all of the enzymes of the glycolytic pathway, only hexokinase and phosphofructokinase were shown to be concentrated in the mitochondrial fraction. All other glycolytic enzymes were found to exhibit higher total and specific activities in the supernatant fraction.
... Although it is generally agreed that brain mitochondria, like mitochondria from other tissues, carry out citric acid cycle oxidations and oxidative phosphorylation, there are varying reports in the literature concerning the relationship of the enzymes of glycolysis to the mitochondrial fraction of brain. Hesselbach and Du Buy (1,2) showed that brain mitochondria convert glucose and glycolytic intermediates to lactate both aerobically and anaerobically. Similarly, Gallagher et al. (3) demonstrated the complete oxidation of glucose and glucose-6-phosphate to carbon dioxide and water by brain mitochondria. ...
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A mitochondrial fraction prepared from calf brain cortex possessed negligible glycolytic activity in the absence of the enzymes of the high speed supernatant fraction. When mitochondria were added to a supernatant system supplemented with optimal amounts of crystalline hexokinase, a 20 per cent stimulation of glycolysis was observed. The supernatant fraction produced minimal amounts of lactate in the absence of exogenous hexokinase; the addition of mitochondria doubled the lactate production. The substitution of glycolytic intermediates for glucose as substrates as well as the addition of exogenous glycolytic enzymes to the supernatant fraction or supernatant fraction plus mitochondria indicated that the mitochondria contributed mainly hexokinase and phosphofructokinase. By direct assay of all of the enzymes of the glycolytic pathway, only hexokinase and phosphofructokinase were shown to be concentrated in the mitochondrial fraction. All other glycolytic enzymes were found to exhibit higher total and specific activities in the supernatant fraction.
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The condition sine qua non for the normal activity of the central nervous system is the continuous production of a sufficient amount of energy. Every function of the nerve cells or of the conducting elements requires either direct or indirect energy. The biochemical processes by which the brain cells derive this energy are very similar to those observed in other organs and in lower forms of life, though slight differences are not uncommon. Thus, for example, unlike most other cell types, the brain cells in vivo appear incapable of using any other substance than glucose as their basic energy source [1]. The carbohydrates play such a dominating part in the energy-producing processes of the nerve cells that it appears appropriate to begin this discussion with the metabolism of glucose.
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A histochemical study on alkaline phosphatase, acid phosphatase, β-esterase, β-glucuronidase, lactic dehydrogenase, glucose-6-phosphate dehydrogenase, succinic dehydrogenase, malic dehydrogenase, isocitric dehydrogenase, glutamic dehydrogenase, α-glycerophosphate dehydrogenase and β-hydroxybutyric dehydrogenase has been carried out to clarify the relationship between the function and morphology of the normal human brain tissues. The materials, 34 in number, were all obtained surgically, and cut at 20μ in -20°C cryostat, then the sections were incubated in each histochemical reaction mixtures. For the histochemical demonstration of hydrolytic enzymes, azo-coupling method was employed, and for the oxidative enzymes, the method described by Pearce with Nitro-BT as the electron acceptor was employed. The following results were obtained; 1) The characteristics of enzyme distribution concerned with glycolysis, aminoacid and fat-metabolism in cerebral tissues were; a) The enzymatic activities in cerebral cortex were generally stronger than those of the medulla. b) The fluctuation of the enzymatic activities were more marked in nervous cells than in other tissues. 2) Alkaline phosphatase and β-esterase activities were exceedingly low in both cerebral cortex and medulla except for some leptomeninx and capillaries. The activities of aminopeptidase were all negative in the brain tissues. 3) In anerobic glycolysis, lactic dehydrogenase activity was very strong in cerbral cortex, and glucose-6-phorphate dehydrogenase activity was relatively weak. 4) In aerobic glycolysis, the activities of succinic, malic and isocitric dehydrogenases were strong in cortex and weak in medulla. Especially isocitric dehydrogenase activity was exceedingly weak. 5) β-glucuronidase activity was rather higher in medulla, and distributed extremely in the periphery of each cells. 6) In cerebellum, nearly all the enzymatic activities were exceedingly strong in Purkinjes' cells. Especially acid phosphatase activity was the strongest in that cells. The enzymatical distribution in other parts of cerebellum was nearly the same in that of cerebrum.
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The glyceraldehyde-3-phosphate and lactic dehydrogenases of both rat liver and Novikoff hepatoma were found to be quantitatively present in the soluble phase of tissue homogenates. In the case of lactic dehydrogenase, cell particulates, notably the microsomes, were able to absorb the enzyme from a medium of low ionic strength and release it upon the addition of salt. This effect gives rise to the presence of a particle-bound lactic dehydrogenase in isotonic sucrose homogenates which is considered to be an artifact.
Colorimetric 535-554, spectrophotometric trioses. A possible andcancers C., pp.162-169, metabolisme determinationof lacticacid in bio-logical material
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