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PubMed1975

Cerebral metabolism in hypoxic hypoxia. I. Pattern of activation of glycolysis: a re-evaluation.

In order to evaluate the pattern of activation of glycolysis in cerebral cortex during hypoxic hypoxia, lightly anesthetized rats were subjected to a lowering of arterial Po2 to about 25 mm Hg and brains were frozen in situ for metabolite analyses either 1, 2, 5, 15 or 30 min following the induction of hypoxia. The lactate and pyruvate concentrations increased progressively during the 30 min period of hypoxia. At 1 and 2 min there were decreases in G-6-P and F-6-P, and increases in FDP, DHAP and 3-PG, indicating activation of phosphofructokinase. At 5 min this pattern of changes was less pronounced and at 15 min it was absent in spite of the fact that the lactate and pyruvate concentrations were further increased. At 30 min F-6-P and F-6-P had further increased but the levels of DHAP, FDP and 3-PG were normal. Evidently, phosphofructokinase activation can only be detected in the early stages of hypoxia, i.e. when the maximal increase in glycolytic flux occurs and before there has been a corresponding activation of other rate-limiting enzymatic steps. Signs of activation of phosphofructokinase were observed in the absence of changes in tissue concentrations of ATP or AMP, with minimal elevation of NH4plus, and in spite of increased (or unchanged) levels of citrate. However, since there were small but significant increases in ADP at 1 and 2 min, and pH-independent decreases in phosphocreatine, the results indicate that hypoxia is accompanied by an initial imbalance between production and utilization of ATP. The metabolic consequences of this imbalance (decrease in phosphocreatine, increases in ADP and P1) may be at least partly responsible for activation of phosphofructokinase.

Adenosine Diphosphate↗
PubMed1976

Effects of fructose-1,6-diphosphate administration on learning efficiency and time sense of the honey bee, Apis mellifica carnica.

In discrimination experiments honey bees had to decide between two glass dishes, one placed on a black cross, the other 40 cm away on a black square. In spontaneous selections the bees in 70% of all cases chose the black cross. The bees were then trained to search back and forth between the cross and the square until after 5 min sugar-water was given on the black square. Over a total of 5 learning trials, during which multiple decisions had been made by the searching insects, 96% of all choices were in favour of the black square. If 80 mM fructose-1,6-diphosphate (F-1,6-P2) in 1 M glucose had been ingested by the bees 30 min before the first spontaneous choice, learning was facilitated with 83% deciding in favour of the black square at the first trial compared with 46% of the controls (which had been fed on 1 M glucose only). In both groups of bees the same number of flight approches was made to the cross or square as made by the bees searching for 5 min before the reward was given. Thus no change in general activity or harvesting motivation appears to be induced by F-1,6-P2. When F-1,6-P2 had been given at the end of a successful learning series the bees favoured the black square for up to 3 days. In contrast to the controls no new incentive needed to be given during this period. Ingestion of other metabolites proved either ineffective, as in the case of fructose-6-phosphate or 5'-adenosine monophosphate, or, as observed after feeding citrate plus 3-phosphoglycerate, even reduced the performance. To test the effect of F-1,6P2 on the same time sense (circadian rhythm), bees were trained on three successive days to visit a feeding place at a specific time of day. The control bees which ingested only glucose on the evening of the 3rd day returned at their entrained 24-h interval on the 4th day. In contrast, the maximum frequency of appearance of bees fed on F-1,6-P2 was advanced by one hour, with minor appearance peaks at earlier hours of the day.

Animals↗
PubMed1976

Metabolic regulations of the rhythmic activity in pacemaker neurons. II. Metabolically induced conversions of beating to bursting pacemaker activity in isolated Aplysia neurons.

In pacemaker neurons of the sea hare Aplysia californica, isolated from their synaptic, ephaptic and humoral inputs, conversion of the regular beating to a bursting discharge pattern can be induced by certain cell metabolites. Administration of the phosphofructokinase (PFK) activator fructose-6-phosphate (F-6-P), or its nonmetabolizable analogue 1-deoxy-F-6-P, induced bursting discharges in R3, R5, R6 and R11 neurons, with spike doublets and triplets appearing transiently in the time pattern. With another PFK activitor, adenosine-5-monophosphate, only double spikes have been noted in R7, R8 and R14 neurons. Burst activity was induced also in the presence of the fructose-1,6-diphosphatase activators, citrate and 3-phosphoglycerate, in R9, R10 and R12 neurons. Cyclic 3',5'-AMP, which also activates the PFK (beside other effects on cellular metabolism), induced bursting discharges in all R3-R14 neurons. In contrast, the inhibitors of the PFK, citrate and ATP, decreased the spike activity of the bursting L3 and L6 neurons, even changing L3 neurons to the regular beating type. Among a variety of cell metabolites tested only pyruvate was able to induce a burst-like tendency in R9 neurons. The characteristic bursting patterns which appeared in the presence of the described metabolic effectors could not be duplicated by low Ca2+ and/or high K+ media nor by artificial shifts in membrane potential triggered by depolarizing and hyperpolarizing currents.

Adenosine Monophosphate↗
PubMed1976

Metabolic regulations of the rhythmic activity in pacemaker neurons. III. Neutralization of the pentylenetetrazol effect in regularly beating Aplysia neurons by metabolic modifiers.

In regular beating pacemaker neurons isolated from the sea hare Aplysia californica, 30-50 mM pentylenetetrazol (PTZ) induces spike doublets and triplets, multi-spike bursts, and paroxysmal depolarizing shifts. The development of the characteristic PTZ-induced changes in impluse pattern is preceded by a transient increase in discharge frequency and a reduction in after-hyperpolarization. According to earlier findings, the rhythmic spike activity of pacemaker neurons is governed by a phosphofructokinase-fructose-1,6-diphosphatase-mediated substrate cycle, the activation of which leads to the appearance of spike bursts. Inhibitory modifiers of this neuronal substrate cycle, such as citrate, ATP, and 3-phosphoglycerate, are able to neutralize the changes in the impluse characteristics occurring as the result of PTZ action. Since the reinitiated single-spike trains reverted again to the PTZ pattern following the further addition of activating modifiers, such as fructose-1,6-diphosphate or fructose-6-phosphate, it appears likely that PTZ exerts an influence on the metabolic reactions driving the rhythmic spike activity. In contrast to the reversible effects of the metabolic modifiers the conventional anti-convulsants, phenobarbital and pentobarbital, merely block all spike activity.

Adenosine Triphosphate↗
PubMed1992

A convenient method for the preparation of a variety of 13C-substituted D-fructose phosphates using readily available enzymes of the glycolytic pathway.

Methods are presented for the preparation of a variety of D-fructose phosphates, 13C-substituted at any single carbon site or at any two symmetrically disposed carbon sites, from either 13C-substituted pyruvate or L-alanine. It is demonstrated that millimole quantities of product can be obtained in good yield following a "one-pot" incubation of 13C-substituted precursors with commercially available enzymes and cofactors of the glycolytic pathway. Since it has previously been shown that a wide variety of aldehydes serve as acceptable substrates for the final rabbit muscle aldolase-catalyzed condensation step, the method can potentially be applied to prepare a wide variety of 13C-substituted sugars and sugar phosphates.

Alanine↗
PubMed1975

The assay of pyruvate kinase activity in gastric mucosa.

Pyruvate kinase activity in gastric mucosal supernatant preparations shows large responses to exogenous effectors. At pH 7.5, fructose 1,6-diphosphate can cause large stimulations in activity. Alanine inhibits the reaction but this effect is partially reversed by fructose 1,6-diphosphate. In the absence of these compounds, 4.0-5.0 mM phosphoenolpyruvate (PEP) is required to generate maximal activity in the assay system used. Electrophoresis reveals an isoenzyme pattern containing only one form of pyruvate kinase, an M isoenzyme, in both fundic and antral mucosa. The pyruvate kinase of gastric mucosa thus resembles the M-type enzymes of leucocytes and liver. Measurements of activity at both 1.0 mM PEP and 4.0--5.0 mM PEP, with and without additions of fructose 1,6-diphosphate, are recommended for the reliable estimation of pyruvate kinase activity in this tissue.

Animals↗
PubMed1975

Enzymatic pattern of glucose metabolic pathways in pyruvate kinase-deficient erythrocytes.

It has been shown that in some cases of congenital non-spherocytic haemolytic anaemia (CNSHA) with pyruvate kinase deficiency, the primary defect may be related to diminished magnesium-stimulated ATPase activity, followed by elevation of the erythrocyte ATP level. ATP as the end product of glycolysis inhibits by negative feedback control the activities of key glycolytic enzymes involved in energy production, i.e. pyruvate kinase (PK) and phosphofructokinase (PFK). Erythrocyte-deficient PK, however, is insensitive to the stimulating effect of fructose 1,6-diphosphate (FDP), which is normally a positive effector of PK. Both competing effectors, i.e. ATP and FDP, seem to show specific interaction. PK, inactive in the presence of high concentrations of ATP, seems to lose its sensitivity to FDP. This effect persists until ATP molecules are present in excess. In vitro incubation of deficient PK with ATPase resulted in increased PK activity as well as in recovery of its sensitivity to the stimulating effect of FDP. The same effects were obtained in vivo by administering magnesium levulinate intravenously to CNSHA patients with PK deficiency. This may indicate that magnesium ions stimulate deficient ATPase activity and lead to diminution of ATP as a negative effector for other regulatory enzymes.

Adenosine Triphosphate↗
PubMed1976

Biphasic reaction kinetics in an anomalous isozyme of erythrocyte pyruvate kinase.

A mutant erythrocyte isozyme of pyruvate kinase (PK) (ATP: pyruvate phosphotransferase, EC 2.7.1.40) has been found in associatin with chronic hemolytic anemia in two siblings who were doubly heterozygous for the isozyme and for quantitative PK deficiency of the usual form. The isozyme was characterized by approximately normal maximum reaction velocities but had markedly decreased affinity for the substrate, phosphoenolpyruvate (PEP), with 5-fold to 10-fold increases in half-saturation constants and decreased interaction between substrate binding sites. Two distinctly separable kinetic patterns for PEP were observed with multiple specimens. Concentrations of fructose 1,6-diphosphate (FDP) required for half-maximal activation were two orders of magnitude greater than controls, and optimal pH was lowered to 6.5. stability at 4 degrees C was markedly decreased, but the lost enzyme could be reactivated by fdp for periods even longer than normal controls.

Adenosine Diphosphate↗
PubMed1976

Defective erythrocyte pyruvate kinase.

A defective pyruvate kinase (EC 2.7.1.40) is described. The abnormal PK is characterized by a shift in the R in equilibrium T equilibrium to the T-state. The Ko.5 for the substrate phosphoenol pyruvate is about 6 times higher than for the normal enzyme, while the KM value for the positive effector Fru-1, 6-P2 is increased. In agreement with a shift to the T-state is the increased affinity of the abnormal enzyme for the negative effectors ATP and alanine. The results are discussed in relation to other abnormal pyruvate kinases.

Adenosine Triphosphate↗
PubMed1977

Heterogeneity of erythrocyte pyruvate kinase deficiency and related metabolic disorders in patients with hematological diseases.

In several patients suffering from congenital non-spherocytic hemolytic anemia or from malignant hemotological disorder associated with erythrocyte pyruvate kinase (PK) deficiency, a metabolic study has been carried out involving the following biochemical determinations: assay of red cell enzyme activities; estimation of glucose consumption; measurement of the rate of glycolytic intermediates; and, in some cases, enzyme purification and characterization of the PK variant. Metabolic equilibrium most probably does not depend on kinetic characteristics of PK molecules. Furthermore, the data obtained allow separation of cases with congenital non-spherocytic hemolytic anemia (hereditary defect) and acquired PK deficiencies.

Adenine Nucleotides↗
PubMed1996

Use of fructose-2,6-diphosphate to assay for phosphofructokinase activity in human muscle.

OBJECTIVE: Use fructose-2,6-diphosphate (fru-2,6-P2) for measuring phosphofructokinase (PFK) activity in muscles. DESIGN AND METHODS: PFK activity was measured at 2 mmol/L MgCl2 and 5 mmol/L adenosine triphosphate (ATP) (mol/L MgCl2:mol/L ATP 0.4) without and with fru-2,6-P2. RESULTS: Human muscle extracts had little PFK activity when assayed at mol/L MgCl2:mol/L ATP of 0.4 to 0.78 without fru-2,6-P2; 1.83 +/- 0.91 units/g muscle. Addition of fru-2,6-P2 produced an immediate 20- to 57-fold increase in activity; 52.8 +/- 12.5 units/g muscle. Raising the mol/L ratio of MgCl2 to ATP to 0.87 and higher without fru-2,6-P2 produced 34%-76% of the PFK activity seen with fru-2,6-P2. A PFK deficiency patient had a trace of activity, which was independent of mol/L MgCl2:mol/L ATP and not activated by fru-2,6-P2. CONCLUSION: The almost complete absence of activity without fru-2,6-P2 at 0.40 mol/L MgCl2:mol/L ATP, and the restoration of maximum activity by fru-2,6-P2 provides an assay for verified PFK activity that could lead to a more accurate diagnosis in patients with PFK deficiency.

Adenosine Triphosphate↗