Hexose Monophosphate Shunt Activity and Oxygen Consumption During Phagocytosis: Temporal Sequence
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Under conditions in which ingestion of labeled bacteria by PMN is accomplished within 10 min, oxygen consumption continues to increase in a linear fashion up to 20 min, while the HMS increase continues for at least 30 min. These results support a mechanism in which the O2 increase precedes the HMS activation.Keywords:
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Abstract We have studied the effects of several different macronutrients on the kinetic behaviour of rat renal glucose 6‐phosphate dehydrogenase (G6PDH) and 6‐phosphogluconate dehydrogenase (6PGDH). Rats were meal‐fed with high‐carbohydrate/low‐protein, high‐protein/low‐carbohydrate and high‐fat diets. High‐protein increased renal G6PDH and 6PDGH activities by 66 per cent and 70 per cent respectively, without significantly changing the K m values of either and each Hexose monophosphate dehydrogenase activity increased steadily, reaching a significant difference on day 4. A rise in carbohydrate or fat in the diets, produced no significant change in either the activity or the kinetic parameters, V max and K m of the two dehydrogenases. In addition, the administration of a high‐protein diet for 8 days significantly increased both the pentose phosphate pathway flux (92·6 per cent) and the kidney weight (35 per cent), whereas no significant changes in these parameters were found when the animals were treated with the other diets. Our results suggest that an increase in the levels of dietary protein induces a rise in the intracellular levels of these enzymes. The possible role of this metabolic pathway in the kidneys under these nutritional conditions is also discussed.
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Phosphogluconate dehydrogenase
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The Metabolism of glucose via glycolysis and the citric acid cycle represents the chief source of energy supplies in the brain. However, enzymes for the metabolism of glucose via the hexosemonophosphate (O'Neill, Simon and Shreeve, 1965) and pentose phosphate (Dreyfus and Moniz, 1962) pathway are also present in brain. A major difficulty in studying intermediates of the hexose and pentose phosphate pathway in brain is their extremely low absolute levels. Recently, fluorimetric, enzymic assays for these substrates have been developed (Kauffman, Brown, Passonneau and Lowry, 1969), and these assays, combined with rapid freezing techniques (Lowry, Passonneau, Hasselberger and Schulz, 1964) have made it possible to study these intermediates in brains of mice. Electrically‐induced tonic‐clonic convulsions are associated with a striking increase in metabolic rate in brain, but phenobarbitone minimizes changes in metabolic rate during convulsions (King, Lowry, Passonneau and Venson, 1967). In order to determine whether or not levels of hexose and pentose phosphates are altered under these conditions, assays for these substrates have been carried out in brains of convulsing mice with or without administration of phénobarbital prior to stimulus.
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Pentose
Carbohydrate Metabolism
Metabolic pathway
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Carbohydrate Metabolism
Ribose
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At the second and third trimesters of pregnancy an increase in activity of hexokinase, glucose-6-phosphate-(G6PD) and 6-phosphogluconate dehydrogenases (6-PDG) occurred simultaneously with a decrease in concentrations of NADPH2 by 26%, ATP by 17% and an increase in NADP by 10-15% in the pregnant women. Total amount of nicotinamide adenine dinucleotide phosphate was unaltered and constituted 0.082-0.075 mmole/L in erythrocytes from both pregnant and nonpregnant women. Activities of hexose monophosphate and glycolytic pathways of glucose metabolism appear to increase in erythrocytes under conditions of normal pregnancy. Concentration of oxidized glutathione tended to increase in the pregnant women, suggesting a possibility of the hexose monophosphate shunt activation.
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Hexokinase
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An immunochemical procedure involving the reaction of liver aldolase antibody and rat liver enzyme preparation shows that conversion of ribose 5-P to hexose 6-P by reactions of the non-oxidative pentose pathway fails to occur in the absence of aldolase activity. Radioautography of pentose pathway products formed by liver enzyme catalysis of [U-14C] arabinose 5-P and unlabelled ribose 5-P illustrates the incorporation of 14C into ketopentose, sedoheptulose, fructose and glucose phosphates. There is approximate congruity of the mole specific radioactivity of the pentose and hexose phosphates. These findings are consistent with the proposal that L-pentose pathway reactions constitute the non-oxidative segment of the pathway in liver.
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Transaldolase
Arabinose
Ribose
Transketolase
Aldolase B
Metabolic pathway
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Pentose
Glucose 6-phosphate
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