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At least 73 records · Page 4Linked to original sources

PubMed2006

Determining and understanding the control of glycolysis in fast-growth tumor cells. Flux control by an over-expressed but strongly product-inhibited hexokinase.

Control analysis of the glycolytic flux was carried out in two fast-growth tumor cell types of human and rodent origin (HeLa and AS-30D, respectively). Determination of the maximal velocity (V(max)) of the 10 glycolytic enzymes from hexokinase to lactate dehydrogenase revealed that hexokinase (153-306 times) and phosphofructokinase-1 (PFK-1) (22-56 times) had higher over-expression in rat AS-30D hepatoma cells than in normal freshly isolated rat hepatocytes. Moreover, the steady-state concentrations of the glycolytic metabolites, particularly those of the products of hexokinase and PFK-1, were increased compared with hepatocytes. In HeLa cells, V(max) values and metabolite concentrations for the 10 glycolytic enzyme were also significantly increased, but to a much lesser extent (6-9 times for both hexokinase and PFK-1). Elasticity-based analysis of the glycolytic flux in AS-30D cells showed that the block of enzymes producing Fru(1,6)P2 (i.e. glucose transporter, hexokinase, hexosephosphate isomerase, PFK-1, and the Glc6P branches) exerted most of the flux control (70-75%), whereas the consuming block (from aldolase to lactate dehydrogenase) exhibited the remaining control. The Glc6P-producing block (glucose transporter and hexokinase) also showed high flux control (70%), which indicated low flux control by PFK-1. Kinetic analysis of PFK-1 showed low sensitivity towards its allosteric inhibitors citrate and ATP, at physiological concentrations of the activator Fru(2,6)P2. On the other hand, hexokinase activity was strongly inhibited by high, but physiological, concentrations of Glc6P. Therefore, the enhanced glycolytic flux in fast-growth tumor cells was still controlled by an over-produced, but Glc6P-inhibited hexokinase.

Animals↗

PubMed1979

Metabolism of carbohydrate derivatives by Pseudomonas acidovorans.

Wild-type Pseudomonas acidovorans strain A1 was unable to grow on glycerol or glucose as sole source of carbon and energy although it grew well on gluconate. Spontaneous glycerol-positive mutants, which apparently had become permeable to glycerol, were readily isolated, but glucose-positive mutants did not occur. P. acidovorans lacked glucose dehydrogenase and glucokinase, which were sufficient to account for its inability to grow on glucose. Gluconate was degraded exclusively via a noncoordinately induced Entner-Doudoroff pathway. Phosphogluconate dehydrogenase was undetectable. In contrast to P. aeruginosa, P. acidovorans possessed a single glyceraldehyde-phosphate dehydrogenase activity, which was NAD+ specific and constitutive, and an inducible pyruvate kinase. Moreover, growth of glycerol-positive strain K2 on glycerol did not induce any of the enzymes related to metabolism of hexosephosphate derivatives as occurs in fluorescent pseudomonads.

Gluconates↗

PubMed1975

Phosphate uptake into organic compounds in skeletal muscle.

Isolated intact frog muscles were incubated in 32-P-labelled Ringer's solution for various periods of time (30 s-20 h). Labelled compounds were isolated from TCA, methanol-chloroform-water, and water extracts of muscle. Hexosephosphates, phosphocreatine, phosphoenolphyruvate, alpha-glycerol phosphate, adenosine triphosphate, and inorganic phosphate were identified after 30 s, and 4 h incubation. Much more labelling was found after 20 h. The incorporation of 32-P in 30 s into organic phosphate compounds, such as alpha-glycerol phosphate and ATP, showed that immediate esterification of Pi occured on, or just inside, the sarcolemma.

Adenosine Triphosphate↗

PubMed2001

Influence of long-term diabetes on renal glycogen metabolism in the rat.

BACKGROUND/AIMS: The effects of acute insulin deficiency on the kidney have been investigated in animal models of experimental diabetes; however, the impact of long-term diabetes has not been determined. METHODS: We measured renal glycogen contents in streptozotocin (STZ)-diabetic rats 3 weeks (n = 12) or 9 months (n = 12) after the induction of diabetes, and in 2 groups of control rats of similar age (n = 16 and n = 12, respectively), in the fed state and after a 24-hour fast. RESULTS: Diabetic rats had high glucose levels, low insulin but normal glucagon concentrations in portal blood. In the fasting state, kidney glycogen content was very low in both young control and young diabetic rats (54 +/- 15 and 189 +/- 26 microg/g, respectively, mean +/- SD); in contrast, glycogen levels were markedly elevated in rats with long-standing diabetes as compared to old nondiabetic animals (2,628 +/- 1,023 +/- and 1,968 +/- 989 microg/g of diabetic rat, fasting and fed, respectively, p < 0.001 vs. 0 +/- 0 and 4 +/- 6 microg/g of control rats). On electron microscopy, large glycogen clusters were localized to the renal tubules. Kidney phosphorylase activity was higher, and synthase activity lower in diabetic than control rats (p < 0.05 for both), whereas kidney glycogen was strongly related to plasma glucose levels, suggesting that the enzyme changes were secondary to glycogen accumulation itself. Renal hexosephosphates and fructose-2,6-bisphosphate contents were both increased in long-term diabetic rats (p < 0.05), implying enhanced fluxes through both glycolysis and gluconeogenesis. CONCLUSION: In chronic, untreated diabetes glycogen accumulates in the renal tubules; prolonged hyperglycemia is the sole driving force for this phenomenon.

Aging↗

PubMed1978

Further studies on creatine kinase activity in human skeletal muscle.

Creatine kinase (CK) was measured in muscle samples from 9 female and 9 male adult subjects using comparatively two procedures. The improved method, using N-acetylcysteine as activator gives results about 1.5 times higher than that with reduced glutathione. The significant correlation existing between activities of CK and hexosephosphate isomerase was confirmed using the improved method. There also exists a correlation between CK and enolase activity. In this respect, there are no differences between muscle samples from male and female subjects.

Adult↗

PubMed1982

Muscle phosphoglycerate mutase deficiency.

A 52-year-old man complained since adolescence of cramps and pigmenturia after 15 to 30 minutes of intense exercise. There was no family history of neuromuscular diseases, and strength was normal. The rise of venous lactate after forearm ischemic exercise was abnormally low. Histochemical and ultrastructural studies of a muscle biopsy showed mild increase of glycogen, which was confirmed by biochemical analysis. Studies of anaerobic glycolysis in vitro showed decrease lactate formation with glycogen and with all hexosephosphate glycolytic intermediates, suggesting a defect below the phosphofructokinase reaction. Muscle phosphoglycerate mutase (PGAM) activity was 5.7% of the lowest control, while all other enzymes of glycolysis had normal activities. Electrophoretic, heat lability, and mercury inhibition studies showed that the small residual activity of PGAM in the patient's muscle was represented by the brain (BB) isoenzyme, suggesting a genetic defect of the M subunit that predominates in normal muscle. The prevalence of the BB isoenzyme in other tissues, including muscle culture, may explain why symptoms were confined to muscle.

Adult↗

PubMed1980

Purification to homogeneity of an insulin-degrading enzyme from human erythrocytes.

The purification of an enzyme is described, a protease, from human erythrocytes which degrades insulin with a high specificity at physiological hormone concentrations. Since the enzyme contains free sulfhydryl groups, affinity chromatography on organomercuri-Sepharose proved to be applicable as a valuable step in the isolation procedure. The purification factor amounted to approx. 6000, the yield to 8%. 1mg of purified enzyme was capable of degrading 50 pmol of insulin/min into trichloroacetic acid-soluble split products. The purified insulin-degrading enzyme was shown to be homogeneous, as demonstrated by gel chromatography, gel electrophoresis and isoelectric focusing. The isoelectric points was at pH 5.8. The molecular weight of nativ enzyme was estimated by gel chromatography and gel electrophoresis and found to be about 150 000-160 000, consisting of 4 subunits. Degradation products of insulin eluted from a Biogel P 30 column are smaller than the A-chain of the hormone, suggesting the activity of a protease. The enzyme appears to be specific for insulin in that it does not degrade other peptide hormones such as growth hormone, prolactin, or thyroid-stimulating hormone. Furthermore, the enzyme does not inactivate enzymes such as lactate dehydrogenase, aldolase, fructose 1,6-bisphosphatase, hexosephosphate isomerase or hexokinase.

Chromatography, Affinity↗

PubMed2001

[Studies on characteristics of kinetics and metabolic shift of genetically engineered yeast Pichia pastoris in high-density chemostat cultivation].

Kinetics and metabolic shift of DNA recombinant yeast Pichia pastoris was studied in high-density chemostat cultivation in which the glycerol was used as a limited substrate. The experimental results showed that (1) cell optical density (OD600) of Pichia pastoris was linear with its dry cell weight (DCW) and wet cell weight (WCW), and reached 100 OD600 = 128.3 g WCW/L or 100 OD600 = 22.9 g DCW/L; (2) The relationship of specific growth rate (mu) and residual concentration of glycerol is accorded with Monod Equation, to obtain mu = mumax S/(Ks + S), where mumax = 0.366 h-1, Ks = 0.1823 g/L. The maximum cell yield of glycerol substrate YG = 0.54 g/g, growth maintaining coefficient m = 0.0069 g/(g.h), The cell yield of oxygen YX/O2 = 30.96 g/moL, and the optimum theoretical dilution rate Dm = 0.341 h-1 by parameter inference; (3) With specific growth rate (mu) increasing, glycerol metablic flux shifts linearly from glycogenesis and hexosephosphate pathways to glycolysis and tricarboxylic acid cycle pathways on basis of variations of consumption rate of NH3.H2O and respiratory quotient value.

Biotechnology↗

PubMedDate not supplied

[Inhibition of glucose in Zajdela hepatoma by 6-phosphogluconate; the role of 3-phosphoglycerate].

Influence of 6-phosphogluconate and 3-phosphoglycerate have been studied for their effect on the fructose-6-phosphate glycolytic transformation reactions in homogenates of the Zajdela hepatoma cells. It is established that 6-phosphogluconate inhibits formation of lactate from fructose-6-phosphate and increases the ratio: dioxyacetone-phosphate/lactate. The influence of 6-phosphogluconate on the formation of lactate from the fructose-1,6-bisphosphate is similar. 3-phosphoglycerate removes the effect of 6-phosphogluconate, its content being unchanged in samples, which indicates rather the regulatory, than the substrate role of 3-phosphoglycerate. Analogous experiments with homogenates of the rat liver show that 6-phosphogluconate inhibits hexosephosphate isomerase, but almost all the introduced substrate (fructose-6-phosphate) is transformed into glucose. Processes of fructose-6-phosphate consumption in the hepatoma and liver are opposite.

Animals↗

PubMed1981

The accumulation of 2-deoxyglucose-6-phosphate activates glycogen synthase (and inactivates glycogen phosphorylase) in rat skeletal muscle.

In the muscle loaded with 2-dGlc "in vitro" (this sugar is accumulated as hexosephosphate) glycogen synthase I levels are changed by a mechanism which is additive to those of hormones such as insulinor epinephrine. The levels of glycogen phosphorylase are decreased only at the highest 2-dGlc-6-P concentration. The role of this effect of sugar phosphate - which has been attributed to the activation of muscle phosphatase (6) - is discussed with regard to glycogen metabolism during muscle function.

Animals↗

PubMed1980

Changes in contractile function and endogenous fuel supply in rat heart upon perfusion with substrate-free medium.

Isolated rat hearts were perfused with aerobic substrate-free medium for different intervals during which changes in functional and metabolic events were examined. The contractile force was maintained for 30 min but thereafter declined toward zero over a period of 90 min. Before the onset of contractile failure, glycogen decreased by 60% of the control value, various intermediates of glycolytic flux, hexosephosphates, and triosephosphates, except dihydroxyacetone phosphate, reached their lowest level, and hydration of the myocardium became maximal. Furthermore, the phosphate potential, creatine phosphate (CrP), ATP, and oxygen consumption decreased by 60%, 45%, 10%, and 18%, respectively, before the onset of contractile failure. A progressive decrease in citrate, isocitrate, alpha-ketoglutarate, and malate was observed during a 2-hr perfusion period, but a slight increase in the levels of oxaloacetate and acetyl-CoA was apparent at 30 and 60 min, respectively. The early phase of contractile failure (30-60 min) was associated with an increase in the free fatty acid (FFA) and AMP levels, whereas the late phase (90-120 min) was characterized by an increase in resting tension and a decrease in oxygen consumption. The complete failure of the heart to generate contractile force at 120 min of perfusion occurred when about 40% of the glycogen and ATP contents and about 25% of the creatine phosphate and triglyceride contents were still present. Therefore, contractile failure of the hearts perfused with substrate-free medium may be caused by an insufficiency of the mechanisms responsible for the mobilization of endogenous glycogen and triglycerides as well as for the generation and utilization of ATP.

Acetyl Coenzyme A↗

PubMed1964