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PubMed1989

Improved brain metabolism with fructose 1-6 diphosphate during insulin-induced hypoglycemic coma.

The effect of fructose 1-6 diphosphate (FDP) on brain metabolism and brain function was investigated in hypoglycemic rabbits. The electroencephalogram and differences in oxygen content of arterial and cerebral venous blood were used as indicators for brain metabolic activity. Hypoglycemic coma was induced and maintained for 1 hour by insulin administration. At the onset of isoelectric EEG, six rabbits were treated with FDP and five rabbits received 0.9% saline. The animals were killed by an overdose of barbiturate 60 minutes after hypoglycemic recovery with glucose. FDP-treated rabbits had lower arterial glucose concentration after 40 minutes of treatment (p less than .05) and a significantly greater difference between the oxygen content of arterial and venous blood after 40 minutes (p less than .01), and after 60 minutes (p less than .025) of FDP infusion than saline-treated rabbits. FDP-treated rabbits also had a lower cerebral glucose-oxygen index than did saline-treated rabbits (p less than .005, after 20 and 40 minutes of FDP infusion). FDP administration was followed by a return of EEG activity during hypoglycemia, whereas saline produced no such effect. After glucose infusion, EEG activity was improved in FDP-treated rabbits; in saline-treated rabbits, minimal or no EEG activity was observed. The data suggest the possibility that, at the doses given in this study, FDP is taken up and used as a metabolic substrate by the brain.

Animals↗
PubMed1986

Effects of fructose-1,6-diphosphate, glucose, and saline on cardiac resuscitation.

Severe hypoxemia causes respiratory and cardiac arrest, in part, because severe hypoxemia decreases glycolysis and adenosine triphosphate (ATP) production by a lactic acid-induced decrease in the activity of phosphofructokinase and glyceraldehyde-3-P dehydrogenase. Fructose-1,6-diphosphate (FDP) administration increases the ATP concentration of blood. The authors hypothesized that FDP might increase the number of rabbits that could be resuscitated from hypoxemic cardiac arrest. To test this hypothesis, heart rate, arterial pressure, left ventricular end-diastolic pressure, and blood gases and pH were measured during normoxemia (FIO2 = 0.21) and again during hypoxemia (FIO2 = 0.04) in 28 adult, white, New Zealand rabbits anesthetized with pentobarbital. With the onset of hypoxemia, we gave either 40 mg/kg of 5% FDP (n = 10), 5% glucose (n = 11), or an equal volume (2.5 ml) of normal saline (n = 7) intravenously and began a continuous infusion of 2.0 mg X kg-1 X min-1 of the same sugar or 0.12 ml/min of saline. FDP-treated rabbits breathed for 20.9 +/- 4.9 (mean +/- SEM) min after initiation of hypoxemia; glucose-treated rabbits breathed for 1.4 +/- 0.2 min, and saline-treated rabbits breathed 10.3 +/- 4 min. Cardiac arrest occurred 2.5 +/- 0.5 min after the onset of respiratory arrest in FDP-treated rabbits, 4.1 +/- 0.2 min in glucose-treated rabbits, and 2.9 +/- 0.4 min in saline-treated rabbits. We could resuscitate all ten FDP-treated rabbits; two of 11 glucose-treated (FDP vs. glucose, P less than 0.001); and one of seven saline-treated rabbits (FDP vs. saline, P less than 0.001) from cardiac arrest.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1990

Fructose 2,6-bisphosphate and carbohydrate metabolism during the life cycle of the aquatic fungus Blastocladiella emersonii.

Removal of the growth medium and resuspension of Blastocladiella emersonii vegetative cells in a sporulation medium resulted in an abrupt fall of fructose 2,6-bisphosphate concentration to about 2% of its initial value within 10 min. The concentrations of hexose 6-phosphate and of fructose 1,6-bisphosphate also decreased by, respectively, three and tenfold over the same period. All these values remained at their low level throughout the sporulation phase and during the subsequent germination of zoospores when performed in the absence of glucose. In contrast, the concentration of cyclic AMP was low during the sporulation period and exhibited a transient increase a few minutes after the initiation of germination. Other biochemical events occurring during sporulation were a 70% reduction in glycogen content and the complete disappearance of trehalose. The remaining glycogen was degraded upon subsequent germination of the zoospores. B. emersonii phosphofructo 2-kinase (PFK-2) and fructose-2,6-bisphosphatase (FBPase-2) could not be separated from each other by various chromatographic procedures, suggesting that they were part of a single bifunctional protein. On anion-exchange chromatography, two peaks of PFK-2 and FBPase-2 were resolved. Upon incubation of fractions from the two peaks or of a crude extract in the presence of [2-32P]fructose 2,6-bisphosphate, two radiolabelled subunits with molecular masses close to 90 and 54 kDa were obtained. The labelling of the subunit of higher molecular mass was greater than that of the lower one in extracts prepared in the presence of protease inhibitors and in the first peak of the Mono Q column. PFK-2 and FBPase-2 displayed kinetic properties comparable to those of mammalian enzymes, but no indication of a cyclic AMP-dependent regulation could be obtained. Phosphofructo 1-kinase and fructose-1,6-bisphosphatase from B. emersonii were, respectively, stimulated and inhibited by micromolar concentrations of fructose 2,6-bisphosphate. The physiological significance of these properties is discussed. A simple method for the determination of trehalose is also reported.

Blastocladiella↗
PubMed1975

Renaturation of acid-denatured rabbit muscle aldolase. Existence and properties of a stable monomeric intermediate.

The effects of temperature, pH and the substrate, fructose 1,6-bisphosphate, upon the kinetics and yield of renaturation of acid-denatured rabbit muscle aldolase have been investigated. The results are discussed in terms of a sequential set of events leading from the unfolded polypeptide chain to the renatured oligomeric enzyme. One of the intermediate molecular species in this sequence has been characterized as a folded monomer with a sedimentation coefficient of 3.1 S. This monomer is shown to be much more heat-labile than the tetramer under identical conditions, thus demonstrating stabilization of the tertiary structure of the polypeptide chain by the quaternary interactions between protomers.

Animals↗
PubMed1976

Studies on the kinetic effects of adenosine-3':5'-monophosphate-dependent phosphorylation of purified pig-liver pyruvate kinase type L.

The effect of cyclic-AMP-dependent phosphorylation on the activity of isolated pig liver pyruvate kinase was studied. It was found that the major kinetic effect of the phosphorylation was to reduce the affinity for the substrate phosphoenolpyruvate, K0.5 for this substrate increasing from 0.3 to 0.9 mM upon phosphorylation. The cooperative effect with phosphoenolpyruvate was enhanced, the Hill constant nH increasing concomitantly from 1.1 to 1.5. V was unaltered. The change in activity occurred in parallel with the phosphate incorporation, except during the initial part of the reaction, when inactivation was correspondingly slower. The affinity for the second substrate ADP was unchanged, with an apparent Km of 0.3 mM at saturating concentration of phosphoenolpyruvate. Likewise, the requirement for potassium was unaffected, whereas the phosphoenzyme required a higher concentration of magnesium ions for maximal activity, compared with the control enzyme. The inhibitory effect of the phosphorylation was counteracted by positive effectors, fructose 1,6-biphosphate in micromolar concentrations completely activated the phosphoenzyme, resulting in an enzyme with properties similar to the fructose 1,6-biphosphate-activated unphosphorylated enzyme, with K0.5 for phosphoenolpyruvate about 0.025 mM and with a Hill constant of 1.1. Hydrogen ions were also effective in activating the phosphoenzyme. Thus, when pH was lowered from 8 to 6.5 the inhibition due to phosphorylation was abolished. The phosphoenzyme was sensitive to further inhibition by negative effectors such as ATP and alanine. 2 mM ATP increased K0.5 for phosphoenolpyruvate to 1.5 mM and nH to 2.3. The corresponding values with alanine were 1.3 mM and 1.9. Phosphorylation is thought to be an additional mechanism of inhibition of the enzyme under gluconeogenetic conditions.

Adenosine Diphosphate↗
PubMed1976

Efficient purification and molecular properties of spinach chloroplast fructose 1,6-bisphosphatase.

A relatively straightforward procedure has been developed for the purification of chloroplast fructose bisphosphatase from spinach leaves to apparent homogeneity and with 80% yield. The molecular weight of the enzyme was about 160 000. Chloroplast fructosebisphosphatase consists of four possibly identical subunits and, at pH 8.8, EASILY DISSOCIATES INTO EQUAL HALVES WITH LOWered activity. Sigmoid saturation curves with Hill coefficients between 3.0 and 3.7 were obtained for fructose 1,6-bisphosphate and Mg2+. Incubation of the enzyme with 20 mM dithiothreitol slowly altered the response to pH from no activity measured at pH 7.5 and full activity at pH 8.8 to equal activity at each of these pH values; at the same time the number of freely available sulphydryl groups increased from four to twelve per molecule. These properties are considered in the context of the observed activation of this enzyme following illumination of chloroplasts.

Chloroplasts↗
PubMed1976

A functional arginine residue in rabbit-muscle aldolase.

Rabbit muscle aldolase is irreversibly modified by the arginine-selective alpha-dicarbonyl, phenylglyoxal, loss of activity correlating with the unique modifications of one arginine residue per subunit, as determined by amino acid analysis, and (7-14C)phenylglyoxal incorporation. The affinity of the modified enzyme for dihydroxyacetone phosphate is significantly reduced while substantial protection against inactivation is afforded by fructose 1,6-disphosphate, dihydroxyacetone phosphate or phosphate ion. The nature of the substrate C-1 phosphate binding site in this enzyme is discussed in the light of these and other results.

Animals↗
PubMed1977

A mathematical model for the influence of anionic effectors on the phosphofructokinase from rat erythrocytes.

The influence of the positive effectors AMP, sulphate, glucose 1,6-bisphosphate and the negative effector 2,3-bisphosphoglycerate on rat erythrocyte phosphofructokinase has been investigated. The kinetic data have been fitted to the Monod-Wyman-Changeux model as well as to a model based on a closed association-dissociation equilibrium. The application of the fitting procedure yeilds for both models a good corresponding between theoretical and experimental data and equal results with respect to the action of the effectors on the enzyme. The corresponding dissociation constants for the binding of the positive effectors to the active state are: AMP 35 micronM, sulphate 0.43 mM and glucose 1,6-bisphosphate 15 micronM. 2,3-Bisphosphoglycerate as in inhibitor stabilizes the inactive state (dissociation constant: 1.4 mM). A preliminary discrimination between the Monod-Wyman-Changeux model and the association-dissociation model has been attempted.

Adenosine Monophosphate↗
PubMed1977

Yeast pyruvate kinase: a mutant from catalytically insensitive to fructose 1,6-bisphosphate.

The paper describes some of the characteristic properties of an altered form of pyruvate kinase from a mutant of Saccharomyces cerevisiae. The partially purified enzyme does not require fructose 1,6-bisphosphate for activity but is stabilised in its presence both at low and at high temperatures. The enzyme displays in the absence of fructose 1,6-bisphosphate hyperbolic kinetics with phosphoenolpyruvate (Km, 0.11 mM), ADP (Km, 0.12 mM) and K+ (Km, 11 mM). Sedimentation velocity experiments indicate that the mutated enzyme and the wild type enzyme have S20,w values of 8.9 and 8.6 S respectively. The mutant with the pyruvate insensitive to fructose 1.6-bisphosphate is capable of growing on synthetic media with alcohol or malate as the sole carbon source. The steady-state intracellular levels of phosphoenolpyruvate in the mutant suggest mechanisms that prevent depletion of this metabolite despite an active pyruvate kinase. Spontaneous reversion of this mutant yields clones with normal enzyme activated by fructose 1,6-bisphosphate.

Adenosine Diphosphate↗