scholarly journals The pentose phosphate pathway of glucose metabolism. Hormonal and dietary control of the oxidative and non-oxidative reactions of the cycle in liver

1969 ◽  
Vol 111 (5) ◽  
pp. 713-725 ◽  
Author(s):  
F. Novello ◽  
J. A. Gumaa ◽  
Patricia McLean
Keyword(s):  
Diabetic Rats ◽  
Pentose Phosphate ◽  
Hexokinase Activity ◽  
Transketolase Activity ◽  
Control Value ◽  
Phosphogluconate Dehydrogenase ◽  
Pentose Phosphate Cycle ◽  
Oxidative Reactions ◽  
Glucose 6 Phosphate Dehydrogenase ◽  
Adrenalectomized Rats

1. Measurements were made of the non-oxidative reactions of the pentose phosphate cycle in liver (transketolase, transaldolase, ribulose 5-phosphate epimerase and ribose 5-phosphate isomerase activities) in a variety of hormonal and nutritional conditions. In addition, glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities were measured for comparison with the oxidative reactions of the cycle; hexokinase, glucokinase and phosphoglucose isomerase activities were also included. Starvation for 2 days caused significant lowering of activity of all the enzymes of the pentose phosphate cycle based on activity in the whole liver. Re-feeding with a high-carbohydrate diet restored all the enzyme activities to the range of the control values with the exception of that of glucose 6-phosphate dehydrogenase, which showed the well-known ‘overshoot’ effect. Re-feeding with a high-fat diet also restored the activities of all the enzymes of the pentose phosphate cycle and of hexokinase; glucokinase activity alone remained unchanged. Expressed as units/g. of liver or units/mg. of protein hexokinase, glucose 6-phosphate dehydrogenase, transketolase and pentose phosphate isomerase activities were unchanged by starvation; both 6-phosphogluconate dehydrogenase and ribulose 5-phosphate epimerase activities decreased faster than the liver weight or protein content. 2. Alloxan-diabetes resulted in a decrease of approx. 30–40% in the activities of 6-phosphogluconate dehydrogenase, ribose 5-phosphate isomerase, ribulose 5-phosphate epimerase and transketolase; in contrast with this glucose 6-phosphate dehydrogenase, transaldolase and phosphoglucose isomerase activities were unchanged. Treatment of alloxan-diabetic rats with protamine–zinc–insulin for 3 days caused a very marked increase to above normal levels of activity in all the enzymes of the pentose phosphate pathway except ribulose 5-phosphate epimerase, which was restored to the control value. Hexokinase activity was also raised by this treatment. After 7 days treatment of alloxan-diabetic rats with protamine–zinc–insulin the enzyme activities returned towards the control values. 3. In adrenalectomized rats the two most important changes were the rise in hexokinase activity and the fall in transketolase activity; in addition, ribulose 5-phosphate epimerase activity was also decreased. These effects were reversed by cortisone treatment. In addition, in cortisone-treated adrenalectomized rats glucokinase activity was significantly lower than the control value. 4. In thyroidectomized rats both ribose 5-phosphate isomerase and transketolase activities were decreased; in contrast with this transaldolase activity did not change significantly. Hypophysectomy caused a 50% fall in transketolase activity that was partially reversed by treatment with thyroxine and almost fully reversed by treatment with growth hormone for 8 days. 5. The results are discussed in relation to the hormonal control of the non-oxidative reactions of the pentose phosphate cycle, the marked changes in transketolase activity being particularly outstanding.

scholarly journals Antioxidant SMe1EC2 modulates pentose phosphate pathway and glutathione-dependent enzyme activities in tissues of aged diabetic rats

2017 ◽  
Vol 10 (4) ◽  
pp. 148-154 ◽  
Author(s):  
Nuray Nuriye Ulusu ◽  
Müslüm Gök ◽  
Arzu Ayşe Sayin Şakul ◽  
Nuray Ari ◽  
Milan Stefek ◽  
...  
Keyword(s):  
Pentose Phosphate Pathway ◽  
Enzyme Activities ◽  
Body Weight Loss ◽  
Diabetic Rats ◽  
Pentose Phosphate ◽  
Aged Rats ◽  
Glutathione S Transferase ◽  
Phosphogluconate Dehydrogenase ◽  
Glucose 6 Phosphate Dehydrogenase ◽  
And Control

Abstract The pentose phosphate pathway and glutathione-associated metabolism are the main antioxidant cellular defense systems. This study investigated the effects of the powerful antioxidant SMe1EC2 (2-ethoxycarbonyl-8-methoxy-2,3,4,4a,5,9b-hexahydro-1H-pyrido[4,3-b] indolinium dichloride) on pentose phosphate pathway (PPP) and glutathione-dependent enzyme activities in aged diabetic and aged matched control rats. Diabetes was induced by streptozotocin injection in rats aged 13-15 months. Diabetic and control rats were divided into two subgroups, one untreated and one treated with SMe1EC2 (10 mg/kg/day, orally) for 4 months. SMe1EC2 ameliorated body weight loss, but not hyperglycemia of aged diabetic rats. Diabetes resulted in decreased glucose-6-phosphate dehydrogenase (G6PD), 6-phosphogluconate dehydrogenase (6PGD) and glutathione-S-transferase (GST), yet in unchanged glutathione reductase (GR) in the liver of aged diabetic rats. In the liver of the aged control rats, SMe1EC2 did not affect G6PDH, 6PGDH and GR, but it inhibited GST. SMe1EC2 also failed to affect diabetes-induced decline in 6PGDH, it ameliorated G6PDH but produced further decline in GST in the liver of aged diabetic rats. In the kidney of aged rats, G6PDH and GST were found to be comparable among the groups, but diabetes up-regulated 6PGDH and GR; these alterations were prevented by SMe1EC2. In the heart of aged diabetic rats, while GST remained unchanged, the recorded increase in G6PD, 6PGD, GR was prevented by SMe1EC2. Furthermore, an unchanged GR and remarkable increases in G6PD, 6PGD and GST were found in the lung of the aged diabetic group. These alterations were completely prevented by SMe1EC2. The results suggest that in aged rats SMe1EC2 can ameliorate the response of the kidney, heart and lung but not that of the liver against diabetes-induced glucotoxicity by interfering with the activity of redox network enzymes.

scholarly journals Regulation of the oxidative phase of the pentose phosphate cycle in mussels

1978 ◽  
Vol 170 (3) ◽  
pp. 577-585 ◽  
Author(s):  
S Rodriguez-Segade ◽  
M Freire ◽  
A Carrion
Keyword(s):  
Inorganic Ions ◽  
Pentose Phosphate ◽  
Oxidized Glutathione ◽  
Phosphogluconate Dehydrogenase ◽  
Pentose Phosphate Cycle ◽  
Intracellular Concentrations ◽  
Glucose 6 Phosphate Dehydrogenase ◽  
Substrate Concentrations

1. The mechanisms that control the oxidative phase of the pentose phosphate cycle in mussel hepatopancreas were investigated. 2. The effects of GSSG (oxidized glutathione) on the inhibition of glucose 6-phosphate dehydrogenase by NADPH [Eggleston & Krebs (1974) Biochem. J. 138, 425-435] extend to 6-phosphogluconate dehydrogenase. 3. The effect of GSSG on both enzymes increases as the [NADP+1]/[NADPH] ratio decreases; greater percentage deinhibition always was obtained for 6-phosphogluconate dehydrogenase. 4. Increasing concentration of GSSG increased the percentage deinhibition. This effect is more pronounced with 6-phosphogluconate dehydrogenase. 5. We confirmed the apparent imbalance between the activities of the two enzymes [sapag-Hagar, Lagunas & Sols (1973) Biochem. Biophys. Res. Commun, 50, 179-185] in the presence of 10mM-Mg2+. 6. The imbalance practically disappears when the substrate concentrations are less than saturating and Mg2+ approaches physiological concentrations. 7. The addition of GSSG at physiological concentrations allows the activities of both enzymes to be measured at high [NADPH]/[NADP+] ratios ratios and the co-operative action of GSSG and Mg2+ on the imbalance between the two enzymes to be verifed. 8. The control of the activity of the two enzymes of the pentose cycle could be carried out by deinhibition of the two dehydrogenases and by the intracellular concentrations of substrates and inorganic ions.

scholarly journals The pentose phosphate pathway of glucose metabolism. Measurement of the non-oxidative reactions of the cycle

1968 ◽  
Vol 107 (6) ◽  
pp. 775-791 ◽  
Author(s):  
F. Novello ◽  
Patricia McLean
Keyword(s):  
Pentose Phosphate Pathway ◽  
Coupled System ◽  
Pentose Phosphate ◽  
Phosphogluconate Dehydrogenase ◽  
Tissue Extracts ◽  
Oxidative Reactions ◽  
Glucose 6 Phosphate Dehydrogenase ◽  
Rate Limiting ◽  
Made In

Methods for the quantitative determination of ribose 5-phosphate isomerase, ribulose 5-phosphate 3-epimerase, transketolase and transaldolase in tissue extracts are described. The determinations depend on the measurement of glyceraldehyde 3-phosphate by using the coupled system triose phosphate isomerase, α-glycero-phosphate dehydrogenase and NADH. By using additional purified enzymes transketolase, ribose 5-phosphate isomerase and ribulose 5-phosphate epimerase conditions could be arranged so that each enzyme in turn was made rate-limiting in the overall system. Transaldolase was measured with fructose 6-phosphate and erythrose 4-phosphate as substrates, and again glyceraldehyde 3-phosphate was measured by using the same coupled system. Measurements of the activities of the non-oxidative reactions of the pentose phosphate pathway were made in a variety of tissues and the values compared with those of the two oxidative steps catalysed by glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase.

Comparison of glycolytic, pentose phosphate pathway, glyoxylate shunt, Krebs' cycle enzymes in Ganeo tigrinum parasitizing hibernating and non-hibernating Rana cyanophlyctis and R. tigrina

1983 ◽  
Vol 57 (1) ◽  
pp. 59-68 ◽  
Author(s):  
P. N. Sharma ◽  
Sushila Mandawat
Keyword(s):  
Isocitrate Lyase ◽  
Krebs Cycle ◽  
Pentose Phosphate ◽  
Glyoxylate Shunt ◽  
Strong Activity ◽  
Key Enzymes ◽  
Phosphogluconate Dehydrogenase ◽  
Weak Activity ◽  
Krebs Cycle Enzymes ◽  
Glucose 6 Phosphate Dehydrogenase

AbstractThe histochemical site and distribution of hexokinase, glycogen phosphorylase (GP Rylase), lactate dehydrogenase (LDH) (key enzymes of glycolysis), glucose-6-phosphate dehydrogenase (GPD) and 6-phosphogluconate dehydrogenase (6PGD) (pentose phosphate shunt enzymes), isocitrate dehydrogenase (IDH), succinate dehydrogenase (SDH), malate dehydrogenase (MDH), and α-ketoglutarate dehydrogenase (α-KDH) (key enzymes of Krebs' cycle), malate synthetase (MS) and isocitrate lyase (IL) (enzymes of glyoxylate shunt) in various tissues of Ganeo tigrinum from hibernating and non-hibernating Rana cyanophlyctis and R. tigrina were studied. Differences in their intensities were revealed. Weak activity of GP Rylase and strong activity of hexokinase in flukes from non-hibernating hosts indicates that they utilize glucose through glycolysis for energy turnover. Intense GP Rylase and weak hexokinase activity in worms from hibernating hosts indicates the utilization of glycogen. Strong activity of IDH, SDH, MDH, α-KGD, MS and IL was demonstrable in the tissues of flukes from non-hibernating hosts, suggesting that Krebs' cycle and glyoxylate shunt, respectively, were operating. Tissues of the fluke from hibernating hosts, on the other hand, displayed positive activity only for SDH and MDH; no activity for MS and IL, the enzymes of glyoxylate shunt, was observed, The activity of the above enzymes was found to be relatively low in worms from hibernating hosts.

THE INFLUENCE OF ADRENALECTOMY UPON THE ACTIVITY OF THE HEXOSEMONOPHOSPHATE SHUNT IN THE LIVERS AND MAMMARY GLANDS OF LACTATING RATS

1960 ◽  
Vol 38 (1) ◽  
pp. 1265-1273 ◽  
Author(s):  
J. S. Willmer
Keyword(s):  
Enzyme Activity ◽  
Considerable Increase ◽  
Mammary Glands ◽  
Mammary Tissue ◽  
Hepatic Tissue ◽  
Phosphogluconate Dehydrogenase ◽  
Growth Changes ◽  
Glucose 6 Phosphate Dehydrogenase ◽  
Adrenalectomized Rats ◽  
Hepatic Level

The development of the hexosemonophosphate shunt in mammary tissue and liver of lactating rats has been studied. A sixfold increase in mammary glucose-6-phosphate dehydrogenase levels between parturition and weaning was accompanied by a considerable increase in 6-phosphogluconate dehydrogenase activity. The hepatic level of the former enzyme was also elevated 11-fold during this period. Adrenalectomy at parturition, or on the 3rd, 6th, 9th, or 14th days of lactation, depressed the activity of this pathway in mammary gland, a lowered level being observed in all cases after operation. A slight increase in enzyme activity was found in hepatic tissue in the immediate postoperative period; this was succeeded by a decrease.These results are discussed in relation to the growth changes observed in groups of unoperated and adrenalectomized rats.

II. Lokalisation von Enzymen des reduktiven und dem oxydativen Pentosephosphat-Zyklus in den Chloroplasten und Permeabilität der Chloroplasten-Membran gegenüber Metaboliten

1967 ◽  
Vol 22 (11) ◽  
pp. 1200-1215 ◽  
Author(s):  
U. Heber ◽  
U. W. Hallier ◽  
M. A. Hudson ◽  
B. von der Groeben ◽  
R. Ernst ◽  
...  
Keyword(s):  
Pentose Phosphate Pathway ◽  
Enzyme Activities ◽  
Intracellular Localization ◽  
Pentose Phosphate ◽  
Oxidative Pentose Phosphate Pathway ◽  
Amino Acid Synthesis ◽  
Phosphogluconate Dehydrogenase ◽  
Chloroplast Membrane ◽  
Glucose 6 Phosphate Dehydrogenase ◽  
Isolated Chloroplasts

1. The interrelationship of metabolic activities in chloroplasts and cytoplasm of leaf cells of spinach, sugar beet and Elodea has been investigated. Different methods have been adopted to study the intracellular localization of enzymes and the flow of phosphorylated intermediates across the chloroplast membrane. The flow of substrates was investigated by determining the rates of the conversion of substrates added to aqueously isolated chloroplasts, prior to and after destruction of the outer chloroplast membrane. The observed differences yielded information as to whether a substrate could traverse the chloroplast membrane.Two methods mere used to investigate the localization of enzymes :a) The percentage distribution of photosynthetic and respiratory enzymes in chloroplasts and cytoplasm was calculated from data on enzyme activities in non-aqueous cell fractions.b) Low levels of enzymes in chloroplasts in the presence of high cytoplasmatic levels were detected by assaying enzyme activities in preparations of aqueously isolated chloroplasts prior to and after ultrasonic destruction of the outer chloroplast membrane.2. If chloroplasts are isolated in aqueous sucrose buffer, their outer membranes act as an efficient barrier against the penetration of NADP, RuDP, GAP and, in some but not all experiments, of FMP and GMP. PGA, DHAP and, probably to a lesser extent, aspartate, ɑ-ketoglutarate, oxaloacetate and FDP can traverse this membrane. Chloroplast membranes are significantly altered when isolated in NaCI-buffer systems and do not correspond to the in vivo situation.3. The conversion of Ri-5-P to RuDP occurs exclusively or nearly exclusively in the chloroplasts indicating that phosphoribulokinase and/or ribosephosphate isomerase are located only there.4. The conversion of Ri-5-P to GAP and SuMP, which is catalyzed by the enzymes ribosephosphate isomerase, xylulosephosphate epimerase and transketolase, proceeds likewise only or at least predominantly in the chloroplasts and not, or only to a small extent, in the cytoplasm.5. The major parts of glucose-6-phosphate dehydrogenase and of 6-phosphogluconate dehydrogenase reside in the cytoplasm. However, a small, but significant, level of these enzymes is to be found also in the chloroplasts. Hexokinase and transaldolase are also present there. Pyruvate kinase and phosphofructokinase appear to be absent from chloroplasts.6. Since, with the presence of glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, hexokinase, transaldolase and enzymes of the Calvin cycle, the enzymic machinery of the oxidative pentose phosphate pathway is complete in the chloroplasts, the results suggest that chloroplasts are engaged in the oxidative decomposition of carbohydrates.7. In the dark the oxidative pentose phosphate pathway requires the control of NADPH formation and the transfer of hydrogen across the chloroplast membrane.8. The available data on the intracellular localization of enzymes and on the kinetics of the distribution of labelled intermediates show that the photosynthetic carbon cycle operates exclusively within the chloroplasts. There is nothing to suggest that enzymes of chloroplasts and cytoplasm cooperate in the cyclic regeneration of the carbon acceptor molecule. However, the existence of phosphorylated transport metabolites suggests that secondary reactions of photosynthesis such as sucrose and amino acid synthesis, which proceed, at least in part, outside the chloroplasts, are directly linked with chloroplastic reactions by activated (phosphorylated) intermediates.

scholarly journals Stimulation of pentose phosphate pathway dehydrogenase enzyme activities in ethionine-treated mice

1968 ◽  
Vol 106 (4) ◽  
pp. 769-776 ◽  
Author(s):  
Hsien-Gieh Sie ◽  
William H. Fishman
Keyword(s):  
Dehydrogenase Activity ◽  
Fold Increase ◽  
Pentose Phosphate ◽  
Hepatic Glycogen ◽  
Synthetase Activity ◽  
Phosphogluconate Dehydrogenase ◽  
Glycogen Synthetase ◽  
Period 2 ◽  
Marked Preference ◽  
Glucose 6 Phosphate Dehydrogenase

1. Mice treated with ethionine (intraperitoneally, 5mg./day for 4 days or 10mg./day for 3 days) showed a profound loss of hepatic glycogen, a decrease of glycogen synthetase activity, a development of hypoglycaemia, a two- to five-fold increase in the activity of glucose 6-phosphate dehydrogenase but no change in 6-phosphogluconate dehydrogenase and an earlier manifestation of the solubilization of phosphorylase as compared with glycogen synthetase. The administration of ATP did not prevent these effects. 2. During the early post-injection period (2–3 days) there was a further enhancement of the activity of glucose 6-phosphate dehydrogenase (tenfold) in the liver and a clear elevation of 6-phosphogluconate dehydrogenase activity (twofold). Subsequently, the glycogen concentration was restored, followed by an earlier reassociation of glycogen particle with phosphorylase than with glycogen synthetase, along with a disappearance of ethionine effect at about the eighteenth day. 3. Glucose 6-phosphate dehydrogenase from both control and ethionine-treated animals showed a marked preference for glucose 6-phosphate as substrate rather than for galactose 6-phosphate, whose rate of oxidation was only 10% of that of the glucose 6-phosphate. 4. Since actinomycin D, puromycin, 5-fluorouracil and dl-p-fluorophenylalanine failed to block the ethionine-enhanced glucose 6-phosphate dehydrogenase activity, the possibility that new enzyme protein synthesis is responsible for the effect is doubtful.

The effect of soaking injury in bean seeds on aspects of the oxidative pentose phosphate pathway in embryonic axes

1992 ◽  
Vol 2 (1) ◽  
pp. 33-39 ◽  
Author(s):  
Johan C. Pretorius ◽  
J. G. Chris Small
Keyword(s):  
Pentose Phosphate Pathway ◽  
Causative Factor ◽  
Pentose Phosphate ◽  
Oxidative Pentose Phosphate Pathway ◽  
Embryonic Axes ◽  
Phosphogluconate Dehydrogenase ◽  
Saturated Water ◽  
Radicle Emergence ◽  
Glucose 6 Phosphate Dehydrogenase ◽  
Seed Coats

AbstractSubmerging Phaseolus vulgaris cv. Top Crop seeds in air-saturated water for 16 h markedly depresses subsequent germination. This is termed soaking injury. Soaking injury does not occur in seeds soaked in CO2-saturated water. Previous studies have shown that soaking injury can be alleviated by drying seeds or removing seed coats. Submergence therefore leads to a situation in bean seeds which is similar to secondary dormancy.As with dormant seeds, C6/C1 ratios of embryonic axes of seeds soaked in air-saturated water remained high (0.8–1.0) during and after soaking. This was paralleled by low activities of glucose-6-phosphate dehydrogenase (EC.1.1.49) and 6-phosphogluconate dehydrogenase (EC 1.1.1.44). In axes of seeds soaked in CO2-saturated water and in unsoaked seeds C6/C1 ratios declined steadily during soaking/imbibition and reached values of around 0.3 after germination. Slight increases ofglucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities occurred in the pre-germination phase. This was followed by a massive increase after radicle emergence. Synthesis of the plastid isoenzymes was a post-germinative event.It appears that soaking injury depresses protein synthesis. Lack of oxidative pentose phosphate pathway activity appears to be a causative factor in soaking injury.

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