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PubMed1983

Inhibition of the pentose phosphate shunt by 2,3-diphosphoglycerate in erythrocyte pyruvate kinase deficiency.

Pentose phosphate shunt activity was studied by the release of 14CO2 from 14C-1-glucose and 14C-2-glucose in the red cells of five patients with pyruvate kinase deficiency and found to be significantly decreased after new methylene blue stimulation when compared to high reticulocyte controls. Incubated Heinz body formation was increased and the ascorbate cyanide test was positive in blood from these patients. The activity of glucose-6-phosphate dehydrogenase (G6PD) as well as that of 6-phosphogluconate dehydrogenase (6PGD) was inhibited to 20% of baseline in normal red cell haemolysate by 4 mM 2,3-diphosphoglycerate at pH 7.1. 2,3-Diphosphoglycerate was a competitive inhibitor with 6-phosphogluconate (Ki=1.05 mM) and a noncompetitive inhibitor with NADP (Ki=3.3 mM) for 6PGD. Since the intracellular concentrations of glucose-6-phosphate, 6-phosphogluconate and NADP are below their Kms for G6PD and 6PGD, the kinetic data suggest that increased concentrations of 2,3-diphosphoglycerate in pyruvate kinase deficient red cells are sufficiently high to suppress pentose phosphate shunt activity. This suppression may be an additional factor contributing to the haemolytic anaemia of pyruvate kinase deficiency, particularly during periods of infection or metabolic stress.

2,3-Diphosphoglycerate↗
PubMed1977

The effect of 6-aminonicotinamide blockade of the pentose phosphate pathway on catecholamines in the rat adrenal medulla, superior cervical ganglion, hypothalamus and synaptosome fractions.

The effect on tissue catecholamines of blockade of the pentose phosphate pathway with 6-aminonicotinamide (6-AN) was studied in the rat. 6-AN at 35-50 mg kg-1 persistently lowered the adrenaline content in the adrenal gland to less than 10% of control values and caused a 50% loss of noradrenaline, which recovered. When the amine turnover rate was increased by a preceding period of drum stress, 6-AN also consistently depressed noradrenaline in the gland. 6-AN was without significant effect on the noradrenaline concentration in heart tissue, hypothalamus and superior cervical ganglion and did not affect the uptake or release of catecholamines in vitro. The possibility is discussed that 6-AN interferes with the biosynthesis of catecholamines, when it blocks the pentose phosphate pathway, by decreasing the supply of reducing equivalents in the form of NADPH which are necessary for the tetrahydropteridine cofactors of tyrosine hydroxylase.

6-Aminonicotinamide↗
PubMed1970

Accessibility of heart water to pentoses.

1. The raffinose space, the inulin space and the weight loss on compression of perfused rat hearts are indistinguishable in magnitude.2. The inulin space shows systematic variations from day to day and is also affected by the procedure used for removing surplus water from the perfused heart. It is therefore not safe to use a mean figure of extracellular space in permeability experiments.3. Perfusion of hearts with arabinose solutions alters the intracellular water content. These alterations can be accounted for if it is assumed that the arabinose which penetrates the cells is uniformly distributed in the cell water.4. By appropriate choice of pentose concentration and of time of perfusion it can be shown that all the estimated cell water is accessible to pentose.5. It is concluded that no detectable fraction of the extracellular water is inaccessible to inulin and that no detectable fraction of the intracellular water is inaccessible to pentose.

Animals↗
PubMed1970

Kinetics of pentose permeation in the perfused rat heart.

1. The fractional permeation of heart cell water by L-arabinose and D-xylose after a standard period of perfusion is less the higher the extracellular pentose concentration.2. At any given pentose concentration the kinetics of permeation are consistent with passive diffusion through the cytoplasm or with transport across the cell membrane by a saturable carrier.3. The concentration dependence of permeation is inconsistent with passive diffusion.4. The kinetics of L-arabinose permeation are consistent with a carrier having V(max) = 2.2 m-mole/l. extracellular water per min and a half-saturation concentration [K] of 0.5 x 10(-4)M. The corresponding figures for D-xylose are V(max) = 1.4, [K] = 1.6 x 10(-4)M.

Animals↗
PubMed1984

Ribose intervention in the cardiac pentose phosphate pathway is not species-specific.

Ribose is cardioprotective in the rat in a variety of pathophysiological conditions. The metabolic basis for this effect is the low capacity of the oxidative pentose phosphate pathway in the myocardium. Ribose bypasses this pathway, elevates the available pool of 5-phosphoribosyl-l-pyrophosphate, and thus stimulates the biosynthesis of adenine nucleotides. In this study reported here the activity of glucose-6-phosphate dehydrogenase, the first and rate-limiting enzyme of the oxidative pentose phosphate shunt, was very low in the human heart and was of the same order of magnitude in the myocardium of various animal species. Furthermore, ribose had a similar stimulating effect on myocardial adenine nucleotide biosynthesis in the guinea pig, in which hemodynamic parameters are different from those in the rat. It is concluded that the metabolic basis for the effectiveness of ribose is similar in all species investigated.

Adenine Nucleotides↗
PubMed1981

Alloxan action on glucose metabolism in cultured fibroblasts. II. Effects on pentose-monophosphate shunt and tricarboxylic acid pathways.

The site of action of alloxan on glucose metabolism has been investigated using cultured human fibroblasts. Analysis of cell extracts after cell monolayers were exposed to D-[U-14C]glucose indicated that the initial stimulation of glucose incorporation by alloxan was observed primarily in the nucleotide fraction (ribose) with inhibition of lactate production. The subsequent inhibition of glucose incorporation was observed in the nucleotide fraction. Assay of 14CO2 production indicated that alloxan enhanced 14CO2 formation from D-[U-14C]glucose for approximately 10 min, followed by inhibition. To probe the site of alloxan action, rates of 14CO2 formation from 1- and 6-position labeled [14C]glucose, and [U-14C]pyruvate were compared. The initial stimulation was observed mainly in D-[1-14C]glucose oxidation, whereas inhibition was measurable with the 6-position tracer and [14C]pyruvate. The results suggest that alloxan initially stimulates the pentose-monophosphate shunt and then subsequently inhibits both the pentose-monophosphate shunt and tricarboxylic acid pathways.

Alloxan↗
PubMed1977

The development of glycolytic and pentose phosphate shunt enzymes in human brain.

A quantitative enzyme analysis of 32 fetal human brains of 6--42 weeks gestational age range was carried out for the major glycolytic and pentose phosphate shunt enzymes. A critical period of raised enzyme levels was observed at 14 weeks. The glycolytic rate was probably controlled by the activities of hexokinase and phosphofructokinase which appear from the development patterns to have independent genetic sites. A rise in most enzyme activities was experienced in the final weeks of gestation towards levels consistent with those of adult tissues. Pentose phosphate shunt enzyme levels remained virtually unchanged during gestation after 14 weeks.

Brain↗
PubMed1983

Glutathione oxidation and activation of pentose phosphate cycle during hydroperoxide metabolism. A comparison of livers from fed and fasted rats.

Perfusion of livers from fed and fasted rats with 0.07--0.1 mM t-butyl hydroperoxide for 15 min decreased the levels of reduced glutathione (GSH) by 1.5 mumol/g liver in both nutritional states. Glutathione disulfide (GSSG) was increased by 70 and 140 nmol/g liver and glutathione mixed disulfides enhanced by 45 and 150 nmol/g liver in livers from fed and fasted animals, respectively. The ratio of GSH/GSSG was decreased from 243 to 58 in fed animals, and from 122 to 8 in fasted animals. The increase of GSSG and the mixed disulfides was nearly parallel until an apparently critical low GSH content of 1.5 mumol/g was reached. Only in livers from fasted rats 14CO2-production from [1-14C]glucose was stimulated upon t-butyl hydroperoxide infusion at the employed rates. Flux of glucose through pentose phosphate cycle rose from 8 to 12% of glucose utilization via glycolysis, whereas in livers from fed animals this portion remained unchanged at 8% Dithio-erythritol reversed pentose phosphate cycle activity as well as GSSG and protein-bound glutathione contents to the original levels. In livers from fasted rats the activity of glucose-6-phosphate dehydrogenase was increased by 34% by t-butyl hydroperoxide infusion.

Animals↗
PubMed1979

Glycolytic, Krebs cycle and pentose phosphate cycle enzymes in spermatozoa of the buffalo (Bubalus bubalis).

Various enzymes of glycolysis (hexokinase, phosphoglucoisomerase, aldolase and lactate dehydrogenase), the Krebs cycle (isocitrate, succinic and malate dehydrogenases), and the pentose phosphate cycle (glucose-6-phosphate and 6-phosphogluconate dehydrogenases) were studied in buffalo spermatozoa by biochemical and cytochemical methods. The enzymes of glycolysis were found to be loosely bound whereas those of the Krebs and pentose phosphate cycles were strongly bound to mitochondrial membranes. All the enzymes studied were localized histochemically in the mid-piece.

Alcohol Oxidoreductases↗
PubMed1979

Development of gluconeogenic, glycolytic, and pentose-shunt enzymes in the chicken kidney.

The activities of the key gluconeogenic, glycolytic, and pentose-shunt enzymes in chicken kidney were determined starting from 8 days before to 58 days after hatching. The activities of pyruvate carboxylase (PC), mitochondrial and cytosolic phosphoenolypruvate carboxykinase (PEPCK), fructose-1,6-diphosphatase (FDPase) and glucose-6-phosphatase (G6Pase) were low in the embryonic tissue but increased towards the time of hatching. After hatching, the activities of PC, mitochondrial PEPCK, and G6Pase continued to increase, but those of FDPase and cytosolic PEPCK decreased. Relatively little change in these activities was observed in chickens over 24 days old. The activities of hexokinase (HK), phosphofructokinase (PFK), pyruvate kinase (PK), and lactate dehydrogenase (LDH) increased during embryonic growth. After hatching, HK activity continued to increase and then decrease, whereas PFK appeared to decrease and then increase to prehatch levels in 28-day-old birds. LDH activity continued to increase until 8 days after hatching and remained constant thereafter. No definite pattern was discernible in the case of PK. As for the pentose-shunt enzymes, there was no significant change in glucose-6-phosphate dehydrogenase activity (G6PDH), but the activity of 6-phosphogluconate dehydrogenase (6PGDH) increased until the chickens were 14 days old and then remained relatively constant.

Animals↗
PubMed1976

[Sedoheptulose-1,7-diphosphate as a source of pentose phosphates in heart muscle].

A possibility and some peculiarities of phosphatase degradation of sedoheptulose-1,7-diphosphate in the myocardium has been demonstrated. The reaction products are inorganic phosphate and sedoheptulose-7-phosphate; the latter product is the substrate of the transketolase reaction during pentose phosphates production. The process is largely localized in the soluble fraction of heart cells; in cellular organelles it is represented in a lesser degree. Possible regulatory mechanisms of pentose phosphate biosynthesis in animal tissues are discussed.

Animals↗
PubMed1986

Biosynthesis of riboflavin. Enzymatic formation of 6,7-dimethyl-8-ribityllumazine from pentose phosphates.

The xylene ring of riboflavin originates by dismutation of the precursor, 6,7-dimethyl-8-ribityllumazine. The formation of the latter compound requires a 4-carbon unit as the precursor of carbon atoms 6 alpha, 6, 7, and 7 alpha of the pyrazine ring. The formation of riboflavin from GTP and ribose phosphate by cell extract from Candida guilliermondii has been observed by Logvinenko et al. (Logvinenko, E. M., Shavlovsky, G. M., Zakal'sky, A. E., and Zakhodylo, I. V. (1982) Biokhimiya 47, 931-936). We have studied this enzyme reaction in closer detail using carbohydrate phosphates as substrates and synthetic 5-amino-6-ribitylamino-2,4-(1H,3H)-pyrimidinedione or its 5'-phosphate as cosubstrates. Several pentose phosphates and pentulose phosphates can serve as substrate for the formation of riboflavin with similar efficiency. The reaction requires Mg2+. Various samples of ribulose phosphate labeled with 14C or 13C have been prepared and used as enzyme substrates. Radioactivity was efficiently incorporated into riboflavin from [1-14C]ribulose phosphate, [3,5-14C]ribulose phosphate, and [5-14C]ribulose phosphate, but not from [4-14C]ribulose phosphate. Label from [1-13C]ribose 5-phosphate was incorporated into C6 and C8 alpha of riboflavin. [2,3,5-13C]Ribose 5-phosphate yielded riboflavin containing two contiguously labeled segments of three carbon atoms, namely 5a, 9a, 9 and 8, 7, 7 alpha. 5-Amino-6-[1'-14C] ribitylamino-2,4 (1H,3H)-pyrimidinedione transferred radioactivity exclusively to the ribityl side chain of riboflavin in the enzymatic reaction. It follows that the 4-carbon unit used for the biosynthesis of 6,7-dimethyl-8-ribityllumazine consists of the pentose carbon atoms 1, 2, 3, and 5 in agreement with earlier in vivo studies.

Candida↗
PubMed1979

NADPH production in the oxidative pentose phosphate pathway as source of reducing equivalents in glycolysis of human red cells in vitro.

Studies have been carried out on human erythrocytes in vitro to clarify the deficit of pyruvate formation under conditions when 2,3 DPG is degraded. The results lead to the conclusion that there exist a cross connection between the glycolytic and the oxidative pentose phosphate pathway which is mediated by the NADP/NADPH couple. NADPH serves as additional reducing equivalent in the reaction of the LDH. In the absence of glucose the pool of the metabolites of the pentose phosphate pathway is able to supply glucose-6-phosphate for the production of NADPH by recombination. The reaction of NADPH at the LDH is probably of significance under in vivo conditions.

Diphosphoglyceric Acids↗
PubMed1979

Studies on cartilage formation XXL Activity of enzymes belonging to the pentose-phosphate cycle in the regenerating articular surface.

The distal articular surface of the femur was removed operatively in 36 dogs. In the regenerating chondrifying articular surface and in the granulation tissue adhering to the capsule glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities were determined 7, 33 and 70 days after operation. In both tissues the activity of these enzymes characteristic of the pentose phosphate cycle ws the highest in the early postoperative stage. This initial increase in activity was followed by a marked reduction in the regenerating articular surface and by a moderate decrease in the tissue adhering to the capsule. For the loss in activity occurring in the chondrifying articular surface, the connective tissue cells (fibroblasts) are responsible. Cartilage precursors and young chondrocytes show a high glucose-6-phosphate dehydrogenase and 6-phosphogluconate activity. Presumably, in the given case of the functions of the pentose-phosphate cycle the NADPH generation and supply of building stones prevail. The activity of these enzymes ws determined in the articular cartilage and in the synovial membrane of the knee joint in further 18 dogs. The activity in the articular cartilage was very slight as compared to that in the synovial membrane.

Animals↗
PubMed1977

[Pentose phosphate pathway and nucleic acid metabolism in red and white muscles of fish].

The activities of the pentose phosphate cycle enzymes, the content of nucleic acids and the activities of acid and alkaline RNAses in the heart and red and white muscles of cartilaginous and teleost fish were determined. It was found that the rates of the dehydrogenase and transferase reactions of the pentose phosphate pathway and the nucleic acid metabolism in the red muscles and heart are much higher than those in the white muscles of the species under study.

Animals↗
PubMed1977

Pentose phosphate pathway and testicular steroidogenesis in rats following oxythiamine treatment.

Suppression of delta5-3beta-hydroxy steroid dehydrogenase (delta5-3beta-OHD) and glucose-6-phosphate dehydrogenase (G-6-P-D) activities along with concomitant stimulation of succinic dehydrogenase (SDH) activity were observed in the rat testicular tissues following treatment with oxythiamine HC1, an inhibitor of pentose phosphate pathway. The same treatment also resulted in an accumulation of cholesterol and ascorbic acid in the gland associated with a decrease in the weights of seminal vesicle and prostate. The results suggest a diminution in testicular steroid biogenesis following an alteration of pentose phosphate pathway.

3-Hydroxysteroid Dehydrogenases↗
PubMed1977

Krebs cycle, pentose phosphate pathway, and glycolysis in the uninvolved gastric mucosa of peptic ulcer and gastric cancer patients.

Uninvolved gastric mucosa from duodenal ulcer, gastric ulcer, and gastric cancer patients was incubated with [1-14C]glucose and [6-14C]glucose in order to assess the relative contributions of the pentose phosphate pathway and Krebs cycle to glucose metabolism. [14C]Glucose counts retained by the tissue, glycolysis, and pyruvate formation were also measured. Tumor tissue from the cancer patients was included in the study. Less than 1.2% of the glucose entering the tissues was metabolized via the pentose phosphate pathway; suggesting that this pathway plays a minor role in energy production from glucose. The major determinant of energy production was the Krebs cycle. Its contribution to glucose metabolism was greatest in the body mucosa of duodenal ulcer patients, less in the uninvolved body mucosa of gastric ulcer patients, and lower still in the corresponding body mucosa of gastric cancer patients. The low levels of Krebs cycle activity seen in the latter tissue resembled those of uninvolved antral mucosa. The smallest Krebs cycle contribution was seen in tumor tissue. [14C]Glucose counts retained by the tissue and glycolysis both tended to vary inversely with Krebs cycle activity among the tissues studied. Thus, both were small in the body mucosa of noncancer patients and somewhat larger in the body mucosa of cancer patients, in uninvolved antral mucosa and in tumor tissue.

Aerobiosis↗
PubMed1976

Cardiac and renal pentose phosphate pathway activity in thiamine deficiency.

Thiamine deficiency was produced in young rats by feeding a thiamine deficient diet. At a time when neurological symptoms were severe, and cardiac and renal transketolase activities were decreased, the animals were sacrificed. Glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities, and flux through the pentose phosphate pathway were similar in pair-fed control and thiamine deficient rats. These data suggest that altered pentose phosphate pathway activity is not a vital feature of murine thiamine deficiency.

Animals↗