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PubMed1985

Protection from ischemic renal injury by fructose-1,6-diphosphate infusion in the rat.

Fructose-1,6-diphosphate (FDP) improves survival in experimental shock. To determine if FDP would protect against single organ damage, rats pretreated with an intravenous infusion of 5% FDP were subjected to 30 minutes of bilateral renal artery occlusion. Controls received an equal volume of a dextrose and sodium chloride solution. Renal function and histology were examined in all groups 24 hours after the insult. Following ischemia, FDP-treated rats had inulin clearances (FDP 897 +/- 129 vs control 349 +/- 59 microliter/min/100 gm BW; P less than 0.01) and solute excretion rates (FDP 6,386 +/- 1,346 vs control 2,602 +/- 396 mOsm/kg/min/100 gm BW; P less than 0.05) greater than control and not different (P-NS) from sham-operated rats. Renal histology was better preserved in the FDP-pretreated group. Thus, pretreatment with FDP provides histologic and functional protection from an ischemic renal insult.

Animals↗
PubMed1985

Allosteric effect of fructose 1,6-bisphosphate on the conformation of NAD+ as bound to L-lactate dehydrogenase from Thermus caldophilus GK24.

The allosteric effect of fructose 1,6-bisphosphate (Fru-1,6-P2) on L-lactate dehydrogenase (L-lactate:NAD+ oxidoreductase, EC 1.1.1.27) from Thermus caldophilus GK24 was studied by means of 1H NMR analyses. The conformation of NAD+ as bound to the T. caldophilus enzyme was elucidated by analyses of the transferred nuclear Overhauser effects (TRNOE), in the presence and the absence of the allosteric effector, Fru-1,6-P2. Upon binding of Fru-1,6-P2 to the enzyme, the ribose ring of the adenosine moiety of NAD+ is converted from the C2'-endo form to the C3'-endo form. This C3'-endo form of the adenosine moiety is similar to that of NAD+ as bound to nonallosteric vertebrate enzymes. However, the anti conformation of the adenine-ribose bond of NAD+ as bound to the T. caldophilus enzyme is not affected by the binding of Fru-1,6-P2. In contrast, the syn conformation of the nicotinamide-ribose bond is converted to the anti form on the binding of Fru-1,6-P2, while the ribose ring remains in the C3'-endo form as found in the case of a nonallosteric enzyme. Such a conformational change of enzyme-bound NAD+ as found on TRNOE analysis is essentially involved in the allosteric regulation of the T. caldophilus enzyme by Fru-1,6-P2.

Adenosine↗
PubMed1979

The breakdown of adenine nucleotides in glucose-depleted human red cells.

1) The rate of 2,3-bisphosphoglycerate breakdown is independent of pH value. 2) The adenine nucleotide pattern at alkaline pH values with its characteristic lowering of ATP and the accompanying accumulation of fructose-1,6-bisphosphate is caused by a relative excess of the activity of the hexokinase-phosphofructokinase system as compared wity pyruvate kinase. 3) The breakdown of adenine nucleotides proceeds via AMP mainly through phosphatase and not via AMP deaminase. 4) The constancy of the sum of nucleotides as long as glucose is present is postulated to be due to resynthesis via adenosine kinase which competes successfully with adenosine deaminase. 5) A procedure is given to calculate ATPase activity of glucose-depleted red cells. The results indicate that the ATPase activity is less at lower pH values and declines with time. An ATPase with a high Km for ATP is postulated. 6) During glucose depletion ATP production is mostly derived from the breakdown of 2,3-bisphosphoglycerate and the supply from the pentose phosphate pool both of which proceed at a constant rate. The contribution of pentose phosphate from the breakdown of adenine nucleotides amounts to 40% of the lactate formed at pH 6.8 and is about twice the lactate at pH 8.1.

Adenine Nucleotides↗
PubMed1979

Modulation of the phosphorylation state of rat liver pyruvate kinase by allosteric effectors and insulin.

The regulation of pyruvate kinase in isolated hepatocytes from fasted rats was studied where the intracellular level of fructose 1,6-bisphosphate was elevated 5-fold by the addition of 5 mM dihydroxyacetone. In this case, flux through pyruvate kinase was increased. The increase in flux correlated with an elevation in fructose bisphosphate levels but not with P-enolpyruvate levels which were unchanged. Pyruvate kinase was activated and its affinity for P-enolpyruvate was increased 7-fold in hepatocyte homogenates. Precipitation of the enzyme from homogenates with ammonium sulfate removed fructose 1,6-bisphosphate and activation was no longer observed. These results indicate that flux through and activity of pyruvate kinase can be controlled by the intracellular level of fructose 1,6-bisphosphate. The effect of elevated fructose 1,6-bisphosphate levels on the ability of glucagon to inactivate pyruvate kinase was also studied where only covalent enzyme modification is observed. Inactivation by maximally effective hormone concentrations was unaffected by elevated levels of fructose 1,6-bisphosphate, but the half-maximally effective concentration was increased from 0.3 to 0.8 nM. Activation of the cyclic AMP-dependent protein kinase by 0.3 nM glucagon was unaffected, but the initial rate of pyruvate kinase inactivation was suppressed. These results suggest that alterations in the level of fructose 1,6-bisphosphate can affect the ability of physiological concentrations of glucagon to inactivate pyruvate kinase by opposing phosphorylation of the enzyme. Consistent with this view was the finding that physiological concentrations of fructose 1,6-bisphosphate inhibited in vitro phosphorylation of purified pyruvate kinase. Inactivation of pyruvate kinase by 0.3 nM glucagon or 1 microM phenylephrine was also suppressed by 10 nM insulin. Insulin did not act by increasing fructose 1,6-bisphosphate levels. The antagonism to glucagon correlated well with the ability of insulin to suppress activation of the cyclic AMP-dependent protein kinase. However, no such correlation was observed with phenylephrine in the absence or presence of insulin. Thus, insulin can enhance pyruvate kinase activity by both cyclic AMP-dependent and independent mechanisms.

Allosteric Regulation↗
PubMedDate not supplied

[Change in aldolase activity in the organs of mice in the process of hepatoma 22a development].

The aldolase activity was measured using two substrates fructose-I-phosphate (FIP) and fructose-1,6-diphosphate (FDP) in the supernatant fraction of homogenates of different mice organs (liver, muscle, brain) and hepatoma tissues during growth of hepatoma 22a. Kinetic parameters Km and Vmax were calsulated. The most essential changes in the activity of aldolase were found during the latent and terminal stares of the hepatoma development. The changes in the aldolase activity observed during development of hepatoma 22a were characterized by altered substrate specificity VFDP /VFIP activity gatio). This ratio was not changed distinctly in liver tissue; in muscles the value decreased from 50 (tumor-free control) to 15 during terminal stages; in brain, to the contrary, it was increased from 20 to 50. The values of Km, Vmax and VFDP /VFIP were similar both in the hepatoma at the eleventh day and in normal brain tissue. The specific inhibition of FDP aldolase activity by ATP was found. Substitution of aldolase B by aldolase AC apparantly ossurred in hepatoma 22a. The data obtained suggest that alteration in the parameters studied may be due to variation in the ration of isozymes.

Animals↗
PubMed1979

[Surgical treatment of experimental liver injuries in dogs with special evaluation of Polish-made cyanoacrylic glue. I. Clinical observations, morphological and biochemical studies of blood and autopsy studies].

Liver wounds were experimentally induced in dogs. The wounds were dressed with catgut suture, suture and fibrinous sponge and ester n-butyl alfa-cyanoacrylic acid in aerosol form obtained laboratorially at the Institute of Organic Chemistry--Polish Academy of Sciences in Warsaw. The basis for evaluation were clinical observations of the operated animals, morphological and biochemical examination of blood and dissection. It was found that the best results were achieved with the surgical glue. Application of this monomer in aerosol form to join and dress liver wounds helps to close them tightly in a short time and obtain full hemostasis and stop bile leaking.

Alanine Transaminase↗
PubMedDate not supplied

[Effect of Ca2+ ions on the pyruvate kinase isoenzymes from rabbit kidney cortex].

Ca2 ions showed the various effect on isoenzymes of pyruvate kinase from rabbit kidney cortex. Ca2 activated the "L" type of pyruvate kinase at low concentrations of PEP and inhibited -- at high concentrations of the latter. "M2" type of pyruvate kinase was inhibited by Ca2 under all the conditions studied. In presence of Ca2+ the activating effect of PDP on "L" and "M2" types of pyruvate kinase was absent; the inhibitory action of ATP on the "M" type of pyruvate kinase was increased at all the concentrations above 1.3 mM. The effect of Ca2+ on the pyruvate kinase isoenzymes depended on content of Mg2+ in the medium.

Adenosine Triphosphate↗
PubMedDate not supplied

[Native and desensitized forms of L-type pyruvate kinase from rabbit kidney cortex].

A time-consuming procedure of isolation of pyruvate kinase isoenzymes from rabbit kidney cortex (more than 5 hrs) at 0-2 degrees led to obtaining of a desensitized form of "L" type, resembling the "M3" type of the enzyme from sceletal muscle. Rapid isolation of pyruvate kinase "L" type (within about 2.5 hrs) at 4-6 degrees provided the isoenzyme in the active (allosteric) form.

Allosteric Site↗
PubMed1984

Hepatic fructose 2,6-bisphosphate in rats with peritonitis and septic shock.

The possible role of inhibited gluconeogenic enzymes in rat liver during preterminal peritonitis septic shock was investigated. There was no difference in maximal activity of the enzymes phosphofructokinase and fructose biphosphatase in septic and control, fasted rats. Rats with sepsis showed a decrease in hexose monophosphates and an increase in fructose biphosphate. There was an unexpected increase in fructose 2,6-bisphosphate despite the hyperglucagonemic state of sepsis. This suggested a dissociation in the coordination of extracellular hormonal and intracellular effector mechanisms in the control of glucose metabolism during the preterminal phase of septic shock. This dissociation may be responsible for the metabolic dyshomeostasis in septic shock.

Animals↗
PubMed1983

Mast cell histamine release induced by doxorubicin and the inhibitory effect of fructose 1,6-diphosphate.

Doxorubicin (DXR) (10(-4) mol/l) causes histamine release from isolated rat mast cells. At lower doses (range 10(-8) mol/l-10(-5) mol/l) the drug failed to evoke secretion. In the 10(-5) mol/l-10(-4) mol/l range there is a significant decrease of the ATP intracellular levels. Fructose 1,6-diphosphate (FDP) produced a sharp increase of the ATP content of the DXR treated cells. In particular, FDP pretreatment inhibited the DXR stimulated histamine release.

Adenosine Triphosphate↗
PubMed1982

Regulation of hepatic phosphofructokinase by 6-phosphogluconate.

6-Phosphogluconate activates phosphofructokinase in extracts of rat liver by decreasing both the apparent S0.5 for fructose 6-phosphate and the degree of cooperative binding of fructose 6-phosphate. There is no effect on the maximum velocity. Enzyme activity is a hyperbolic function of the concentration of 6-phosphogluconate, and the apparent Km is 60 microM. Thus, a substantial activation of the enzyme is achieved with a physiological concentration of 6-phosphogluconate (40 microM). Activation of phosphofructokinase by 6-phosphogluconate is influenced by a low molecular weight factor(s) in liver extracts. Part of the influence may be attributed to fructose 2,6-bisphosphate which, in some conditions, acts synergistically with 6-phosphogluconate to activate phosphofructokinase. In the presence of a mixture of ATP, ADP, and AMP at physiological concentrations, the effects of 6-phosphogluconate (40 and 200 microM) and a saturating concentration of fructose 2,6-bisphosphate (400 nM) are more nearly additive. This result suggests that 6-phosphogluconate and fructose 2,6-bisphosphate act at different sites on the enzyme and that 6-phosphogluconate may contribute to the physiological regulation of hepatic phosphofructokinase. Regulation of phosphofructokinase by 6-phosphogluconate may provide a means by which the disposition of glucose 6-phosphate between the oxidative branch of the hexosemonophosphate pathway and glycolysis can be coordinated, an effect which may be important during hepatic lipogenesis.

Animals↗