Control of reduced diphosphopyridine nucleotide oscillations in beef heart extracts. 3. Purification and kinetics of beef heart phosphofructokinase

Analysis of the dynamics of relaxation type oscillation in glycolysis of yeast extracts

In yeasts, the glycolysis may display oscillations of its metabolites while it is converting glucose. The dynamics of the oscillations has been investigated in cytoplasmic extracts of yeast under relaxation type conditions by determining the time course of some of the glycolytic metabolites. The compounds of the nucleotide pool have been identified as fast variables and the glucose derivatives as slow variables of the relaxation type. The period of oscillation has been subdivided into four phases which represent prominent parts of the limit cycle in the phase plane of a slow versus a fast variable. From the reaction processes in these phases, a dynamical picture of the mechanisms of oscillations is suggested. Accordingly, the oscillation results from an alternating activity of the fructose bisphosphate and the polysaccharide synthesis, both of which are coupled to glycolysis via the nucleotide pool. The processes in the phases are analyzed by calculating the rates of the reaction steps in the biochemical pathway.

The phase relationship of glycogen and free fatty acids in tissues of aestivating giant African snails (Achatina achatina)

The phase relationships of glycogen and free fatty acids (FFA) in the digestive (midgut) gland, foot muscle and heart muscle of starved and aestivating giant African snails (Achatina achatina) were analysed by means of phase plane plots. Phase plane plots of glycogen against FFA content indicated that these metabolites were out of phase in the digestive gland but in phase in the foot muscle, whereas the plot for the heart muscle had a long axis parallel to the abscissa. Digestive gland glycogen was out of phase with foot muscle FFA and with heart muscle FFA. Phase plane plots of foot muscle glycogen digestive gland FFA had its long axis parallel to the abscissa, whereas the plot of foot muscle glycogen against heart muscle FFA showed that these metabolites were in phase. Heart muscle FFA was in phase with either foot muscle FFA or digestive gland FFA. Pyruvate kinase extracted from the foot muscle of starved and aestivating snails was very labile and behaved like the allosteric type by exhibiting co-operative interaction with respect to phosphoenolpyruvate, allosteric activation by fructose 1,6-diphosphate and inhibition by ATP. The oscillatory motions of glycogen and FFA are discussed in terms of anaerobic metabolism in aestivating snails.

Dynamic aspects of insulin action: synchronization of oscillatory glycolysis in isolated perifused rat fat cells by insulin and hydrogen peroxide

Glucose oxidation to CO2 was investigated in isolated perifused rat epididymal fat cells. Insulin stimulated rates of oxidation up to 30-fold. Multiple pulses of insulin or prolonged perifusion with the hormone led to a time-dependent desensitization of the cells. The action of insulin could be mimicked by H2O2. Reversal of H2O2 effects was associated with a damped oscillation of large initial amplitude. Initiation of perifusion with insulin induced rates of glucose oxidation that oscillated around a mean elevated rate with an amplitude of about +/- 4% of the mean, significantly larger than the measurement error. Basal rates did not show clear oscillations. The oscillations after insulin had a statistically significant period of around 14 min. The results were the same with C1- or C6-labeled glucose and occurred in the presence of both 0.275 and 5.5 mM glucose in the perifusion medium. The oscillations were interpreted as the result of insulin- or H2O2-induced synchronization of oscillatory glycolysis by individual fat cells. The similarity of the observed oscillatory period with the period of oscillatory insulin secretion by pancreatic beta cells suggests that oscillatory glycolysis may constitute the internal pacemaker for the latter process.

Interaction of D-fructose and fructose 1-phosphate with yeast phosphofructokinase and its influence on glycolytic oscillations

Fermentation of D-fructose- and D-glucose induced glycolytic oscillations of different period lengths in Saccharomyces carlsbergensis. Recent studies suggested, that D-fructose or one of its metabolites interacted with phosphofructokinase (ATP:D-fructo-6-phosphate 1-phosphofructokinase, EC 2.7.1.11), the core of the glycolytic 'oscillator'. In order to explore the kinetics of interaction, the influence of D-fructose and fructose 1-phosphate on purified yeast phosphofructokinase was studied. D-fructose concentrations up to 0.3 mM stimulated the enzyme, while a further increase led to competitive inhibition. The Hill coefficient for fructose 6-phosphate decreased from 2.8 to 1.0. Fructose 1-phosphate acted in a similar way, up to 1 mM activation and inhibition competitive to fructose 6-phosphate at higher concentration (2.0--3.5 mM) with the same effect on the Hill coefficient. The inhibition patterns obtained with D-fructose or fructose 1-phosphate suggest a sequential random reaction mechanism of yeast phosphofructokinase with fructose 6-phosphate and MgATP2-. The mode of interaction of phosphofructokinase with D-fructose and fructose 1-phosphate is discussed. The influence of both effectors resulted in altered enzyme kinetics, which may cause the different period lengths of glycolytic oscillations.

Fructose-1,6-bisphosphate, a regulator of metabolism

Fructose-1,6-bisphosphate affects the rate of a large variety of enzyme reactions. In some instances its role as a physiologic effector is well documented. In many cases the effects of fructose bishosphate on particular enzymes have been demonstrated in vitro but the link to physiologic conditions has not yet been established. It is the purpose of this paper to summarize the scattered findings in fructose bisphosphate as an effector of enzyme reactions and to draw some conclusions about the role of the compound in metabolic regulation.

A comparison of the properties of the phosphofructokinases of the fat body and flight muscle of the adult male desert locust

1. Phosphofructokinase was isolated, and partially purified by ammonium sulphate fractionation, from the fat body and flight muscle of the desert locust. 2. Ammonium sulphate appears to stabilize the enzymes, but does not activate them. 3. Both flight-muscle and fat-body enzymes give sigmoidal hexose monophosphate concentration-activity curves, which are characteristic of regulatory enzymes. 4. At low ATP concentrations both the enzyme activities increase rapidly with increasing ATP concentrations, but above an optimum concentration ATP becomes inhibitory. This optimum concentration is 0.2mm for the fat-body enzyme and 0.1mm for the flight-muscle enzyme. 5. AMP activates both the enzymes; half-maximal activation occurs at 10mum in each case, the effect being independent of substrate concentration. 6. 3',5'-(cyclic)-AMP (0.5mm) and P(i) (1mm) activate the flight-muscle enzyme, but have no effect on the fat-body enzyme. 7. FDP (1mm) inhibits both enzymes, and with the flight-muscle enzyme this inhibition is increased by increasing the ATP concentration. 8. Citrate, phosphoenolpyruvate and alpha-glycerophosphate have no effect on either enzyme under the assay conditions used. 9. The properties of phosphofructokinases from the locust are compared with those of phosphofructokinases from other sources.