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Effect of exogenous fructose-1,6-bisphosphate on glycolysis in the isolated perfused rat heart.

To test the mechanism of action of fructose-1,6-bisphosphate (F-1,6-P2), experiments were conducted on isolated perfused rat hearts to measure the glycolytic rate supported by exogenous glucose with simultaneous measurement of oxygen consumption and the release of lactate and pyruvate. Glycolysis was assayed in terms of the release of tritiated water from [5-3H] glucose, a measure of the rate through the aldolase step. It was found that 5 mmol/L F-1,6-P2 reduced the glycolytic rate parallel to the decrease in oxygen consumption. The results suggest that the cardioprotective action of F-1,6-P2 is related to a substrate effect and a decrease in adenosine triphosphate consumption as indicated by a decrease in oxygen consumption in accordance with the recent demonstration of Ca2+ binding by F-1,6-P2.

Animals↗

Hemodynamic and electrocardiographic effects of fructose-1,6-diphosphate in acute myocardial infarction.

Acute hemodynamic and electrocardiographic effects of fructose-1,6-diphosphate (FDP), an agent that is supposed to restore anaerobic glycolytic flux in the ischemic myocardium, were studied in 40 patients with acute myocardial infarction who were grouped into 4 subsets: subset 1, normal (15 mm Hg or less) pulmonary artery (PA) wedge pressure and normal (35 g-m/m2 or greater) left ventricular (LV) stroke work index; subset 2, elevated (more than 15 mm Hg) PA wedge pressure and normal LV stroke work index; subset 3, normal PA wedge pressure and reduced (less than 35 g-m/m2) LV stroke work index; subset 4, elevated PA wedge pressure and LV stroke work index moderately reduced to a range between 16 and 34 g-m/m2. Patients were randomized into an FDP (250 mg/kg body weight in isotonic saline solution intravenously in 20 minutes) and into a placebo group. Each subset contained 5 FDP- and 5 placebo-treated patients. After basal measurements, hemodynamic measurements were reassessed at 60, 90 and 120 minutes from the infusions, while a standard 12-lead electrocardiogram was recorded in the basal state and 120 minutes after infusion. Nonsignificant hemodynamic change was observed in the placebo subsets, and FDP failed to exert any effect in subsets 1, 2 and 3. A 24% (p less than 0.02) increase in cardiac index occurred 60 minutes after FDP in subset 4. LV stroke work index also increased, while PA wedge pressure remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

A method for the synthesis of D-3-phospho[U-14C]glycerate.

An enzymatic method for the synthesis of radioactive D-3-phosphoglycerate from commercially available D-[U-14C]fructose 1,6-diphosphate is described. The unique aspect of this procedure is the substitution of arsenate for phosphate in the glyceraldehyde-3-phosphate dehydrogenase reaction. The 1-arseno-3-phosphoglycerate formed spontaneously hydrolyzes to form the D-3-phosphoglycerate product. The methods detailed below for the synthesis, isolation, and analysis of the 3-phospho[U-14C]glycerate product are relatively easy.

Carbon Radioisotopes↗

A competitive binding assay for fructose 2,6-bisphosphate.

A new direct assay method for fructose 2,6-bisphosphate has been developed based on competitive binding of labeled and unlabeled fructose 2,6-P2 to phosphofructokinase. Phosphofructokinase (0.5-1.3 pmol protomer) is incubated with saturating concentrations (5.0-5.5 pmol) of fructose 2,6-[2-32P]P2 and samples containing varying concentrations of fructose 2,6-P2. The resulting stable binary complex is retained on nitrocellulose filters with a binding efficiency of up to 70%. Standard curves obtained with this assay show strict linearity with varying fructose 2,6-P2 in the range of 0.5 to 45 pmol, which exceeds the sensitivity of most of the previously described assay methods. Fructose 2,6-P2, ATP, and high concentrations of phosphate interfere with this assay. However, the extent of this inhibition is negligible since their tissue contents are one-half to one-tenth that examined. This new assay is simple, direct, rapid, and does not require pretreatment of tissue extracts.

Animals↗

The separation of [32P]inositol phosphates by ion-pair chromatography: optimization of the method and biological applications.

We have developed an ion-pair reverse-phase HPLC method to measure inositol phosphates in 32P-labeled cells. The different chromatographic parameters were analyzed to optimize the resolution of the 32P-labeled metabolites. Analysis of inositol phosphates in biological samples was improved by a single charcoal pretreatment which eliminated interfering nucleotides without removing inositol phosphates. The kinetics of production of inositol phosphates in calcium-activated erythrocytes, vasopressin-stimulated hepatocytes, and thrombin-activated platelets were analyzed. Original data on the activation of phosphoinositide phospholipase C were obtained in intact erythrocytes by direct measurement of inositol (1,4,5)P3. Data from agonist-stimulated hepatocytes and platelets were consistent with those from previous studies. In conclusion, this technique offers many advantages over the methodologies currently employed involving anion-exchange chromatography and [3H]inositol labeling: (i) 32P labeling is less expensive and more efficient than 3H labeling and can be used with all types of cells without permeabilization treatments and (ii) ion-pair HPLC gives good resolution of inositol phosphates from nucleotides with shorter retention times, and long reequilibration periods are not required.

Blood Platelets↗

An endpoint enzymatic assay for fructose 2,6-bisphosphate performed in 96-well plates.

An endpoint enzymatic assay for fructose 2,6-bisphosphate based on the ability of the compound to stimulate pyrophosphate 6-phosphofructo-1-kinase and performed in a 96-well plate is reported here. The method presents a low detection limit and a high sensitivity that could be further improved; moreover, the use of 96-well plates greatly increases the number of samples that can be simultaneously assayed.

Enzyme-Linked Immunosorbent Assay↗

A method for the determination of changes of glycolytic metabolites in yeast on a subsecond time scale using extraction at neutral pH.

Glucose metabolism in yeast can be stopped within 0.1 s by spraying the cells in 60% methanol at -40 degrees C. With this procedure the integrity of the cells is not damaged. Using stopped-flow equipment for the incubation with glucose, major changes within a second are shown to occur in intracellular glucose-6-phosphate whereas the fructose-1,6-bisphosphate concentration remains constant. After quenching, the cells can be separated from the medium, washed with cold methanol when required, and extracted using chloroform at -40 degrees C at neutral pH, ensuring minimal degradation of labile metabolites. With partly automated enzymatic methods, a large variety of metabolites, including all glycolytic intermediates, can be determined in the neutral extracts. During the first second after addition of glucose, a significant increase in free intracellular glucose is found.

Chloroform↗