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PubMed2004

Effect of fructose-1,6-bisphosphate in the cold storage solution after 12 and 36 hours of rat liver preservation.

Fructose-1,6-bisphosphate (FBP) has been reported to have a protective effect on liver injury following ischemic/reperfusion periods because it maintains ATP levels during cold preservation. In the present study, we evaluated the effects of addition of FBP to storage solutions for cold liver preservation during 12 or 36 hours. Adult male Wistar rats were randomly divided into three experimental groups. The hepatic perfusion and preservation were performed with these solutions: UW; UW plus 10 mmol/L FBP; and FBP 10 mmol/L (FBPS) alone. The biochemical measurements of AST and ALT were performed on samples of the cold storage solution after 12- or 36-hour preservation. UW and FBPS solutions showed similar preservation grades at 12 hours. Addition of 10 mmol/L of FBP to UW solution induced liver injury and a poor preservation grade during 12 or 36 hours. UW solution was better than FBPS after 36 hours preservation. UW solution continues to offer a superior performance for liver preservation during long times; however, FBPS may be an alternative for short cold preservation times.

Adenosine↗
PubMed1997

Hemodynamic effects of fructose 1,6-diphosphate in patients with normal and impaired left ventricular function.

We compared the short-term hemodynamic effects of intravenous fructose 1,6-diphosphate (FDP) administration in patients with coronary artery disease. Hemodynamic measurements were performed before and after administration of FDP in two groups of patients: those with impaired left ventricular (LV) function, elevated LV end-diastolic pressures (LVEDP > or =12 mm Hg, n = 30), and those with normal LV function (LVEDP <12 mm Hg, n = 17). In those with impaired LV function, FDP induced a decrease in LVEDP from 22 +/- 1.31 to 16.73 +/- 1.46 mm Hg (p< 0.0001). The cardiac index increased (2.50 +/- 0.11 to 2.81 +/- 0.13 L/m2 [p < 0.0001]), as did the LV stroke work index (31.7 +/- 2.04 to 40.3 +/- 2.67 gm x m x m2 [p < 0.0001]). FDP induced no significant change in heart rate and mean aortic pressure. Pulmonary pressure and resistance declined (p<0.002 and p< 0.0001, respectively). Systemic vascular resistance decreased because of increased cardiac output and unchanged arterial pressure (p < 0.001). In those patients with normal baseline LVEDP (5.06 +/- 0.27 mm Hg), FDP decreased heart rate (p< 0.0001) and systemic and pulmonary resistance (p < 0.03 and p < 0.004, respectively), whereas LVEDP and mean aortic and pulmonary pressures remained unchanged. FDP moderately increased cardiac output (p < 0.05), stroke volume index, and LV stroke work index (p< 0.002 and p< 0.003, respectively). The observed improvement in LV function in those patients with elevated LV filling pressures is thought to be a result of an increased energy production by the Embden-Meyerhoff pathway and to act as a positive inotrope.

Cardiac Catheterization↗
PubMed1983

Metabolic and functional effects of carbohydrate substrate with single-dose and multiple-dose potassium cardioplegia.

The isolated working rat heart model of ischemic arrest was used to determine if the addition of carbohydrate substrate to our cardioplegic solution enhanced metabolic and functional myocardial protection. A single-dose cardioplegia technique, as used in earlier studies that showed glucose to have a harmful effect, and a multidose technique similar to that used clinically were studied and compared. Because recent data suggest that fructose-1,6-diphosphate(FDP) may have a protective effect with ischemia, this substrate was also tested and compared to glucose and fructose. In this model, single-dose cardioplegia resulted in poor protection from ischemic injury in all study groups. There was marked improvement in myocardial protection with multidose cardioplegia, and further substantial protection of myocardial function, high-energy phosphate levels, and glycogen stores when carbohydrate substrate was added to the arrest solution. The solution with a higher concentration of glucose (0.5%) provided the best overall metabolic and functional recovery and was clearly superior to fructose and FDP, both of which had about the same protective effect. Improved protection with carbohydrate substrate was accompanied by evidence of substantial increase in glycolytic flux, supporting the idea that increased anaerobic glycolysis can help protect the ischemic myocardium when intermittent reinfusion of cardioplegic solution is done.

Adenosine Triphosphate↗
PubMed2003

Fluorescence study of ligand binding to potato tuber pyrophosphate-dependent phosphofructokinase: evidence for competitive binding between fructose-1,6-bisphosphate and fructose-2,6-bisphosphate.

The intrinsic fluorescence of potato tuber pyrophosphate:fructose-6-phosphate 1-phosphotransferase (PFP) was used as an indicator of conformational changes due to ligand binding. Binding of the substrates and the allosteric activator fructose-2,6-bisphosphate was quantitatively compared to their respective kinetic effects on enzymatic activity. PFP exhibited a relatively high affinity for its isolated substrates, relative to the enzyme's respective K(m) (substrate) values. There are two distinct types of fructose-1,6-bisphosphate interaction with PFP, corresponding to catalytic and activatory binding. Activatory fructose-1,6-bisphosphate binding shares several characteristics with fructose-2,6-bisphosphate binding, indicating that both ligands compete for the same allosteric activator site. Activation by fructose-1,6-bisphosphate or fructose-2,6-bisphosphate was exerted primarily on the forward (glycolytic) reaction by greatly increasing the enzyme's affinity for fructose-6-phosphate. Binding of substrates and effectors to PFP and PFP kinetic properties were markedly influenced by assay pH. Results indicate an increased glycolytic role for PFP during cytosolic acidification that accompanies anoxia stress.

Binding, Competitive↗
PubMed1990

Regulation of muscle phosphofructokinase by physiological concentrations of bisphosphorylated hexoses: effect of alkalinization.

To clarify the role of glucose-1,6-P2, fructose-2,6-P2 and fructose-1,6-P2 in the control of the glycolytic flux during muscle contraction, we have determined the activity of muscle phosphofructokinase in the presence of physiological concentrations of these bisphosphorylated hexoses and other allosteric effectors, and at increasing pH values. In the presence of fructose-2,6-P2, both glucose-1,6-P2 and fructose-1,6-P2 can additionally activate the enzyme and partially counteract citrate inhibition. Activation of phosphofructokinase produced by alkalinization increases in the presence of the bisphosphorylated hexoses. It is suggested that the hexose bisphosphates could play a significant role in the initial burst of the glycolytic flux during muscle contraction, when an alkaline pH shift is produced.

Animals↗
PubMed1992

Effects of epidermal growth factor on glycolysis in A431 cells.

A431 cells were treated with epidermal growth factor (EGF) to study the mechanism by which this factor accelerates the glycolytic flux. After EGF treatment, fructose-2,6-bisphosphate (Fru-2,6-P2) levels rose up to 2-fold. This change correlated with an increase in phosphofructokinase-2 activity, which was not due to a change in the transcription or translation of the enzyme, neither in the amount of enzyme. PK-C does not appear to be involved in the signalling mechanism since EGF was equally potent in PK-C depleted cells than in control cells. The increase in Fru-2,6-P2 levels was lower and more transient in cells treated with EGF in a calcium-free medium than in the presence of the cation, and it was restored by the addition of calcium to the medium. These results suggest a possible role for calcium-mediated pathways in the control of Fru-2,6-P2 levels in A431 cells.

Calcium↗
PubMed1991

An inositol phosphoglycan stimulates glycolysis in human platelets.

Upon hydrolysis of membrane glycosyl-phosphatidylinositol (gly-PtdIns), an inositol phosphoglycan (IPG) is generated, responsible for multiple biological activities and recently proposed as mediator of the action of a variety of hormones and growth factors. The present study shows that IPG is able to significantly stimulate platelet glycolysis, which represents the major energy producing pathway in this cell system. The activation of glycolytic flux induced by IPG appears to be specific and very rapid even though the molecular mechanism involved remains to be elucidated.

Blood Platelets↗
PubMed1983

Similarity of activation of yeast phosphofructokinase by AMP and fructose-2,6-bisphosphate.

Phosphofructokinase from yeast is effectively activated by AMP and fructose-2,6-bisphosphate by increasing the affinity of the enzyme to fructose-6-phosphate and the maximum activity toward this substrate. The enzyme is activated by AMP and fructose-2, 6-bisphosphate both at high and at low concentrations of ATP. The half maximum stimulation concentrations of AMP and fructose-2, 6-bisphosphate are about 200 microM and 2 microM, respectively. At saturating concentrations of AMP and fructose-2, 6-bisphosphate similar maximum activities were observed in the dependence of enzyme activity on the concentrations of fructose-6-phosphate. The fructose-6-phosphate affinity is more enhanced by fructose-2, 6-bisphosphate than by AMP.

Adenosine Monophosphate↗
PubMed1984

Changes in fructose-2,6-bisphosphate levels after glucose loading of starved rats.

Fructose-2,6-bisphosphate levels in freeze-clamped livers of starved rats were 0.5 nmol/g liver. Oral administration of 1 g glucose per kg body weight to starved rats increased glycogen levels from 4 mg/g liver to 13.5 mg/g in 2 hr but did not significantly alter fructose-2,6-bisphosphate levels. The low level of this effector is consistent with an active gluconeogenic process and the results support the hypothesis that carbon atoms for glycogen synthesis can be derived from 3-carbon precursors via this pathway, even in the presence of glucose.

Animals↗
PubMed1985

The reactive cysteine residue of pig kidney fructose 1,6-bisphosphatase is related to a fructose 2,6-bisphosphate allosteric site.

Modification of a highly reactive cysteine residue of pig kidney fructose 1,6-bisphosphatase with N-ethylmaleimide results in the loss of activation of the enzyme by monovalent cations. Low concentrations of fructose 2,6-bisphosphate or high (inhibitory) levels of fructose 1,6-bisphosphate protect the enzyme against the loss of monovalent cation activation, while non-inhibitory concentrations of the substrate gave partial protection. The allosteric inhibitor AMP markedly increases the reactivity of the cysteine residue. The results indicate that fructose 2,6-bisphosphate can protect the enzyme against the loss of potassium activation by binding to an allosteric site. High levels of fructose 1,6-bisphosphate probably inhibit the enzyme by binding to this allosteric site.

Animals↗
PubMed1986

Effect of tolbutamide on fructose-6-phosphate,2-kinase and fructose-2,6-bisphosphatase in rat liver.

The effects of tolbutamide on the activities of fructose-6-phosphate,2-kinase and fructose-2,6-bisphosphatase were examined using rat hepatocytes. Tolbutamide stimulated fructose-6-phosphate,2-kinase activity and inhibited fructose-2,6-bisphosphatase activity, resulting in an increase of fructose-2,6-bisphosphate level. Changes in the activities of the enzyme by tolbutamide were due to variation in the Km value, but not dependent on alteration of Vmax. Glucagon inhibition of fructose-2,6-bisphosphate formation resulting from an inactivation of fructose-6-phosphate,2-kinase and an activation of fructose-2,6-bisphosphatase was released by tolbutamide. Tolbutamide stimulation of fructose-2,6-bisphosphate formation through regulation of fructose-6-phosphate,2-kinase/fructose-2,6-bisphosphatase may produce enhancement of glycolysis and inhibition of gluconeogenesis in the liver.

Animals↗
PubMed1986

Pyrophosphate-dependent sucrose metabolism and its activation by fructose 2,6-bisphosphate in sucrose importing plant tissues.

In the presence of pyrophosphate and uridine diphosphate, sucrose was cleaved to form glucose 1-phosphate and fructose with soluble extracts from sucrose importing plant tissues. The glucose 1-phosphate then was converted through glycolysis to triose phosphates in a pyrophosphate-dependent pathway which was activated by fructose 2,6-bisphosphate. Much less activity, less than 5%, was found in sucrose exporting tissue extracts from the same plants. These findings suggest that imported sucrose is metabolized in the cytoplasm of plant tissues by utilizing pyrophosphate and that sucrose metabolism is partially regulated by fructose 2,6-bisphosphate.

Biological Transport↗
PubMed1986

Fructose 2,6-bisphosphate in human platelets: its possible role in the control of basal and thrombin-stimulated glycolysis.

Human platelets contain fructose 2,6-bisphosphate, 6-phosphofructo-l-kinase (ATP: D-Fructose-6-phosphate-1-phosphotransferase, E.C.2.7. 1.11), the rate-limiting enzyme in platelet glycolysis appear to be significantly activated by physiological concentration of the compound, suggesting for fructose 2,6-bisphosphate a key regulatory role in the control of the glycolytic flux. Incubation of human platelets with thrombin results in a parallel and rapid increase of fructose-2,6-bisphosphate levels and glycolytic flux, suggesting that the compound may also be involved in the enhancement of glycolysis elicited by the stimulating agent.

Blood Glucose↗
PubMed1987

Effect of chronic uremia on fructose 2,6-bisphosphate glycolytic and gluconeogenic enzymes in rat liver.

The level of fructose 2,6-bisphosphate and the maximal activities of key gluconeogenic and glycolytic enzymes were determined in the liver of a rat model of chronic uremia and in ad libitum-fed control and pair-fed control animals. Fructose 2,6-bisphosphate was decreased in uremia and its level negatively correlated with the concentration of blood urea nitrogen. The changes in gluconeogenic enzymes in uremic rats were not different from those in the pair-fed controls. However, pyruvate kinase was decreased in uremia when compared to both controls. These studies offer a possible mechanism for the role of the liver in the carbohydrate intolerance of uremia.

Animals↗
PubMed1988

Activation of muscle phosphofructokinase by alpha-glucose 1,6-bisphosphate and fructose 2,6-bisphosphate is differently affected by other allosteric effectors and by pH.

Citrate, ATP and AMP affect similarly the activation of muscle phosphofructokinase by alpha-glucose 1,6-bisphosphate and fructose 1,6-bisphosphate, but they affect differently its activation by fructose 2,6-bisphosphate. Activation by alpha-glucose 1,6-bisphosphate and fructose 2,6-bisphosphate is also differently affected by pH. This suggest that both alpha-glucose 1,6-bisphosphate and fructose 1,6-bisphosphate induce the same conformational change on muscle phosphofructokinase, distinct from that produced by fructose 2,6-bisphosphate.

Adenosine Monophosphate↗