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At least 1,495 records · Page 83Linked to original sources
PubMed1994

Effect of anoxia on isolated turtle tissues: is the response to anoxia mediated by protein kinase second messengers?

Organ slices from the turtle Trachemys scripta elegans were incubated under aerobic and anoxic conditions to examine the effect of protein kinase (PrK) second messengers in potentiating the biochemical responses to anoxia exposure. Incubating liver slices from aerobic animals under anoxic conditions produced biochemical changes exactly similar to those observed in vivo: phosphofructokinase (PFK) was more sensitive to citrate inhibition and the percentage of glycogen phosphorylase (GP) in the active a form increased. On the other hand, incubating brain and heart tissue slices under anoxic conditions produced no changes in PFK and GP kinetic constants. Addition of PrK second messengers (dibutyryl-cAMP or Ca2+ plus phorbol myristate acetate) to the incubated tissues did not promote anoxia-associated changes in aerobically incubated tissues nor did they prevent anoxia-associated changes in anaerobically incubated tissues. These results suggest that unidentified external hormonal signals mediate heart and brain responses to anoxia. It is also apparent that cAMP and Ca2+ plus phospholipid do not play a role in bringing about the anoxia-induced changes in PFK, GP and fructose 2,6-bisphosphate in liver of turtles.

Aerobiosis↗
PubMed1995

[Fructose-2,6-bisphosphate system and experimental states].

The molecular mechanisms of the inhibitory action of fructose- 2,6-bisphosphate (F-2,6-P2) on fructose-1,6-biphosphatase (FB-Pase-1), the key enzyme of gluconeogenesis, and the those of the activating action of F-2,6-P2 on phosphofructo-1-kinase (PFK-1), the key enzyme of glycolysis, NMR spectroscopy first provided direct evidence for the fact that F-2,6-P2 was involved in the regulation of the sedoheptulose cycle of a nonoxidative stage of the pentosephosphate pathway. Procedures were developed in measuring the levels of F-2,6-P2 in the cell of experimental animal tissues and human blood lymphocytes. Naturally different emergencies substantially affected the F-2,6-P2 system by triggering these or those mechanisms controlling the activity of enzymes of this system. Vanadium-containing compounds were demonstrated to have a positive action on carbohydrate metabolism in diabetic (streptozotocin-induced) rat hepatocytes.

Animals↗
PubMed1993

[A pharmacological study of the hepatoprotective activity of fructose-1,6-diphosphate].

A fructose-1,6-diphosphate preparation was tested for hepatoprotective activity through biochemical and morphologic studies in experiments on Wistar rats sustaining D-galactosamine- and paracetamole-induced hepatotoxicity. Findings indicated the modeled hepatic lesions to be readily reproducible, to simulate some characteristics of human liver pathology, and to be suitable for testing substances expected to have hepatoprotective action; intraperitoneal administration of fructose-1,6-diphosphate at a dose of 1000 mg/kg body weight proved moderately protective against liver damage by D-galactosamine; the benefit observed concerned mostly dystrophic and inflammatory changes in the liver; in a number of cases, correlation was noted between biochemical serum parameters and pathomorphologic liver alterations.

Acetaminophen↗
PubMed1994

Glucose-stimulated synthesis of fructose 2,6-bisphosphate in rat liver. Dephosphorylation of fructose 6-phosphate, 2-kinase:fructose 2,6-bisphosphatase and activation by a sugar phosphate.

The effect of glucose on hepatic fructose (Fru) 2,6-P2 in starved rats was investigated. When livers were perfused with high glucose (40 mM), hexose-P in the liver increased immediately reaching the maximum within in 2 min, but Fru 2,6-P2 after a lag period of 4 min increased linearly. The activation of Fru 6-P,2-kinase and inactivation of Fru 2,6-Pase also showed a similar lag period. Determination of the phosphate contents of the bifunctional enzyme after 10 min of glucose perfusion revealed that 90% of the enzyme was in the dephospho form while only 10% of the control liver enzyme was dephosphorylated. Comparison of crude extracts of liver perfused with either high glucose or normal glucose (5.6 mM) showed that high glucose livers contained 50% higher protein phosphatase activity, which dephosphorylated the bifunctional enzyme. Subcellular fractionation of the extract showed that activation of the protein phosphatase occurred in the cytosol. Desalting of the cytosolic fraction resulted in a 50% loss of the protein phosphatase activity. The low molecular weight activator in the cytosol was isolated, and by various chemical and enzymatic methods it was identified as xylulose 5-P. The activation of protein phosphatase by xylulose 5-P showed a highly sigmoidal saturation curve. The rate of formation of xylulose 5-P in the perfused liver showed a lag period of approximately 2 min, and after 4 min its concentration reached 10 microM, the minimum concentration necessary for the activation of the protein phosphatase. We conclude that the mechanism of glucose-induced Fru 2,6-P2 synthesis was not due to increased Fru 6-P as generally thought but occurred as a result of dephosphorylation of Fru 6-P,2-kinase:Fru 2,6-Pase. Moreover, the dephosphorylation was enhanced by increased xylulose 5-P, which activated a specific protein phosphatase. The results suggest a mechanism for coordinated regulation of glycolysis and the pentose shunt pathway that is mediated by xylulose 5-P.

Animals↗
PubMed1994

Shared active sites of fructose-1,6-bisphosphatase. Arginine 243 mediates substrate binding and fructose 2,6-bisphosphate inhibition.

The active site of pig kidney fructose-1,6-bisphosphatase (EC 3.1.3.11) is shared between subunits, Arg-243 of one chain interacting with fructose-1,6-bisphosphate or fructose-2,6-bisphosphate in the active site of an adjacent chain. In this study, Arg-243 was replaced by alanine using techniques of site-specific mutagenesis and the cloned pig kidney enzyme expressed in Escherichia coli. Compared with wild-type enzyme, kinetic parameters of the altered enzyme characterizing catalytic efficiency, magnesium binding, and inhibition by AMP differed but by less than an order of magnitude; affinity for substrate fructose 1,6-bisphosphate was 10-fold poorer, and affinity for inhibitor fructose 2,6-bisphosphate was 1000-fold poorer. Molecular dynamics simulations were undertaken to determine possible alterations in active sites of the enzyme due to replacement of Arg-243 by Ala and suggested that in the mutant enzyme loss of one cationic group leads to reorganization of the active site especially involving lysine residues 269 and 274. The differences in properties of the mutant enzyme indicate the key importance of Arg-243 in the function of fructose-1,6-bisphosphatase and confirm on a functional basis the shared active site in this important metabolic enzyme.

Adenosine Monophosphate↗
PubMedDate not supplied

Effect of intravenous fructose-1,6-diphosphate on myocardial contractility in patients with left ventricular dysfunction.

STUDY OBJECTIVE: To examine the effects of fructose-1,6-diphosphate on myocardial performance using nuclear scintigraphy. DESIGN: Prospective, randomized, single-blind, parallel study. SETTING: Urban teaching hospital clinical research center. PATIENTS: Individuals with New York Heart Association functional class II-III heart failure (mild to moderate). INTERVENTIONS: Subjects received either intravenous fructose-1,6-diphosphate 125 mg/kg or normal saline 1.3 ml/kg every 12 hours over 10 minutes for four consecutive doses. Left ventricular performance was assessed by radionuclide ventriculography at baseline and within 60 minutes after the fourth infusion. Vital signs were monitored throughout the study period. MEASUREMENTS AND MAIN RESULTS: Fructose-1,6-diphosphate resulted in a modest 7% increase in left ventricular ejection fraction (p < 0.05). Peak ejection rate and peak diastolic filling rate did not change significantly. There were no changes in blood pressure or heart rate with either fructose-1,6-diphosphate or placebo. CONCLUSIONS: Fructose-1,6-diphosphate produces a modest but significant increase in left ventricular ejection fraction in patients with mild to moderate heart failure.

Adult↗
PubMedDate not supplied

[The use of pyrophosphate-dependent phosphofructokinase for the determination of fructose-2,6-bisphosphate concentration in biological material].

The authors discuss methods for purification of pyrophosphate fructose-6-phosphate phosphotransferase from potato tuber and enzymatic method for measuring fructose-2,6-biphosphate concentration in isolated hepatocytes of normal and diabetic rats and come to a conclusion on a higher sensitivity of the method they propose in comparison with the method making use of commercial phosphofructokinase from rabbit muscles. Their method may be used for fructose-2,6-biphosphate measurements in various biologic materials.

Animals↗
PubMed1994

[Protective effect of 1,6-diphosphate fructose in ischemic renal failure in elderly rats].

To study the protective effect of 1,6-diphosphate fructose (FDP) on acute ischemia damage in brain, heart and liver, we observed its effect on acute ischemic renal failure (AIRF). AIRF in male Wistar rats was produced by renal arterial clamping for 45 minutes and reperfusion for 90 minutes. The rats were divided into 4 groups according to their age and FDP therapy: G1: young (3-4 months) AIRF rats without FDP; G2: old (26-27 months) AIRF rats without FDP; G3: young AIRF rats with FDP (0.5g/kg) i.v. infusion; G4: old AIRF rats with FDP. Inulin clearance (CIn), PAH clearance (CPAH), urinary sodium (UNA) were examined before ischemia and 30, 60 and 90 minutes after reperfusion. After reperfusion for 90 minutes, renal cortex was taken for the examination of renal mitochondrial ATP synthetic content (miATPs). CIn and CPAH were lower in G2 than in G1 (0.24 +/- 0.12 vs. 1.75 +/- 0.79, P < 0.01; 0.87 +/- 0.42 vs 7.12 +/- 4.04, P < 0.05, at 90 minutes reperfusion). CIn and CPAH in G1 showed an auto-recovery up to 40.1% and 33.7% of the level in contrast to G2. In G3 and G4 original FDP infusion resulted in a significant increase in miATPs and CIn (609 +/- 145 vs 389 +/- 97; 569 +/- 77 vs 338 +/- 61, P < 0.02; 2.47 +/- 0.58 vs 1.75 +/- 0.79, 1.29 +/- 0.42 vs 0.24 +/- 0.12, P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Kidney Injury↗
PubMed1994

Insulin-like actions of tungstate in diabetic rats. Normalization of hepatic glucose metabolism.

Oral administration of tungstate for 15 days normalized glycemia in streptozotocin-induced diabetic rats. Simultaneously, the alterations in hepatic glucose metabolism due to diabetes were almost completely counteracted by this treatment. Thus, 6-phosphofructo-2-kinase, L-pyruvate kinase, and glycogen phosphorylase alpha activities reached levels similar to those observed in healthy animals. Hepatic levels of fructose 2,6-bisphosphate and glycogen also recovered. However, the recovery of glucokinase activity and hepatic levels of glucose 6-phosphate was only partial. The total activity of glycogen synthase increased, although the activation state was not recovered. Moreover, mRNA levels of hepatic glucokinase, glycogen phosphorylase, and phosphoenolpyruvate carboxykinase were also normalized. Tungstate administration in healthy animals also affected all these parameters, although to a much lesser extent. All these effects were similar to those previously reported for vanadate, suggesting a common mechanism of action in vivo.

Animals↗
PubMedDate not supplied

[Characterization of free and bound pyruvate kinase in the brain of the teleost fish mullet].

Activity of pyruvate kinase free and bound with the structural components that has been revealed in brain of red mullet. The bound form disappeared as a result of 1.5 hour hypoxia. The Hill coefficients for phosphoenolpyruvate and ADP of the both enzyme forms were about 1, but the Michaelis constants of free enzyme for the phosphoenolpyruvate and ADP were 2-3 times higher than that for the bound form. The pH-dependence of the both enzymes was similar. The free enzyme was studied as a result of heating probes at 45 degrees C during 15 minutes, but the bound form was successively activated and stabilized within this procedure. The ATP inhibition of the both forms was the same. Fructose-1,6-bisphosphate and alanine does not affect the pyruvate kinase activity. Possible mechanisms for regulation of kinetic properties and redistribution of pyruvate kinase between free and bound states are discussed.

Adenosine Diphosphate↗
PubMed1993

[Anoxia-reperfusion injury to endothelial cells: mechanism and protection].

Endothelial cells in the aortic walls of inbred SD rats were cultured in MEM culture medium containing 10% calf serum, and an anoxia-reperfusion injury model was established. The effect of anoxia-reperfusion injury on cultured endothelial cells was studied by measurements of membrane fluidity, intracellular Ca content, the release rate of 51Cr and the uptake rate of trypan-blue. The effect of fructose 1-6 diphosphate (FDP) and captopril (Cap) on cultured endothelial cells was also investigated. The findings indicated that the two drugs might protect cultured endothelial cells from anoxia-reperfusion injury. The mechanism of anoxia-reperfusion injury and the protective effect of the two drugs on cultured endothelial cells were briefly discussed.

Animals↗
PubMedDate not supplied

[Level of fructose-2,6-bisphosphate and activity of fructose-1,6-bisphosphatase in hepatocyte suspensions in streptozotocin diabetes].

Content of fructose-2,6-bisphosphate was drastically decreased (about 5-fold) in hepatocyte suspension obtained from rats with streptozotocin-induced diabetes, as compared with that of control animals. At the same time, activity of fructose-1,6-bisphosphatase was increased 2-fold in these hepatocytes. Incubation mixture of the hepatocytes from the diabetes impaired animals contained only low amounts of lactate.

Animals↗
PubMed1993

Effect of aging on insulin regulation of fructose 2,6-bisphosphate metabolism in human fibroblasts.

Fructose 2,6-bisphosphate (Fru-2,6-P2) content in human fibroblasts is under hormonal control and is strictly related to glycolytic flux. In the present study it has been examined whether aging process is accompanied with an impairment in the control exerted by insulin on the metabolite content. Upon insulin stimulation old fibroblasts show a reduced increase in Fru-2,6-P2 content and glycolytic flux. Similarly, 6-phosphofructo-2-kinase (PFK-2) activity in old fibroblasts is increased at a lesser extent by insulin treatment, suggesting that an impairment at post-receptor level in the signalling pathway of insulin might occur with aging. In addition in unstimulated senescent fibroblasts PFK-2 displays higher activity and reduced Km for substrate, suggesting either that during senescence PFK-2 undergoes a post-translational modification or that a different PFK-2 isoenzyme is expressed.

Cell Line↗
PubMed1993

[The effect of fructose-1,6-diphosphate and phosphoenolpyruvate on the course of early occlusion and reperfusion arrhythmias in rats].

Fructose-1,6-diphosphate (150 and 50 mg/kg) and phosphoenolpyruvate (0.5 and 0.1 mg/kg) decreased the development of ventricular tachycardia, ventricular fibrillation and the intensity of ventricular extrasystoles after coronary occlusion in experimental rats. Both compounds were active as anti-fibrillation agents on reperfusion arrhythmias. Fructose-1,6-diphosphate potentiated the effect of lidocaine.

Animals↗
PubMed1993

The effect of fructose on fructose 2,6-bisphosphate level and fructose 6-phosphate, 2-kinase activity in the perfused rat liver.

In order to investigate the effect of fructose on the metabolic rates of liver glycolysis, changes in fructose 2,6-bisphosphate content and fructose 6-phosphate, 2-kinase (F6P2kinase) activity were examined using perfused rat liver. When the starved liver was perfused with 0.5 mM fructose, the fructose 2,6-bisphosphate level was 6.66 nmol/g liver, or the maximum. However, with further increases in the fructose concentration, increments in the fructose 2,6-bisphosphate level gradually decreased. F6P2kinase was inactive in the starved rat liver. By perfusion with the medium containing fructose or even without fructose, however, the enzyme was activated. The suppression of the increase in the fructose 2,6-bisphosphate level by perfusion at higher fructose concentrations was at least partly due to the inhibition of F6P2kinase by F1P.

Adenosine Triphosphate↗