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W Schellenberger

Publications and source records attributed to W Schellenberger.

At least 55 records · Page 3Linked to original sources
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↗
PubMed1983

Diminution of stationary enzyme activities at increases of pyruvate kinase concentration in a reconstituted enzyme system.

In a homogeneous and open enzyme system containing phosphofructokinase, pyruvate kinase, adenylate kinase, and glucose 6-phosphate isomerase the consequences of variations of the enzyme concentrations on the stationary enzyme activities have been investigated. An unexpected behavior was observed upon variation of the maximum activity of pyruvate kinase. Depending on the experimental conditions an increase of the concentration of pyruvate kinase resulted either in a diminution or in a stimulation of the stationary activity of this enzyme. An increase of the maximum activity of phosphofructokinase, however, stimulates both the activities of phosphofructokinase and pyruvate kinase. The experimental results are interpreted in terms of a mathematical model, based on the kinetic properties of the enzymes involved. The correlation between the observed changes of the activities of phosphofructokinase and pyruvate kinase and the appearance of multiple stationary states is discussed.

Adenylate Kinase↗
PubMed1983

Oscillations in the phosphofructokinase-fructose 1,6-bisphosphatase cycle. I. Purification and kinetic characterization of fructose 1,6-bisphosphatase from pig liver.

A rapid and effective purification procedure for pig liver fructose 1,6-bisphosphatase in neutral form is described. The procedure involves heat treatment and chromatography with CM-Sephadex with specific elution of the enzyme by fructose 1,6-bisphosphate and AMP. The enzyme was found suitable for integration into a reconstituted enzyme system in which the generation of oscillations is investigated. The kinetic properties of fructose 1,6-bisphosphatase are studied under conditions compatible to those applied for the investigation of the dynamic behaviour of the reconstituted system (pH 6.6, presence of inorganic phosphate). The enzyme is significantly inhibited by AMP and fructose 6-phosphate. The substrate fructose 1,6-bis phosphate has a high affinity to the enzyme and was found weakly inhibiting even at high concentrations. The kinetic results are interpreted in terms of a mathematical model which reflects the interaction of the various effectors with the enzyme.

Animals↗
PubMed1983

Oscillations in the phosphofructokinase--fructose 1,6-bisphosphatase cycle. II. Influence of fructose 1,6-bisphosphatase on the character of oscillatory states.

The dynamic behaviour of an open futile cycle composed of phosphofructokinase and fructose 1,6-bisphosphatase has been investigated in a homogeneous reconstituted enzyme system in which the two enzymes cooperate with pyruvate kinase, adenylate kinase and glucose 6-phosphate isomerase. By the kinetic cooperation of phosphofructokinase and fructose 1,6-bisphosphatase various types of dynamic patterns can be generated. In the absence of fructose 1,6-bisphosphatase oscillations do not occur. As experimentally demonstrated, in a definite region of maximum activities of fructose 1,6-bisphosphatase sustained oscillations originate while at higher concentrations of the enzyme damped oscillations appear. At increasing concentrations of fructose 1,6-bisphosphatase damping is strengthened. Finally, at very high concentrations of fructose 1,6-bisphosphatase the metabolites relax monotonously to the stationary states. The observed oscillatory phenomena are mainly caused by the antagonistic effects of AMP on the kinetics of phosphofructokinase and fructose 1,6-bisphosphatase.

Adenylate Kinase↗
PubMed1982

Transitions between alternate ATP-producing and ATP-consuming stationary states in a reconstituted enzyme system containing phosphofructokinase.

The kinetic behavior of a reconstituted eyzyme system containing purified phosphofructokinase, pyruvate kinase, adenylate kinase, and glucose 6-phosphate isomerase was investigated. Experimentally the approach is based on a stirred flow-through reactor containing gel entrapped enzymes. The experiments were performed on the basis of a mathematical model developed from the kinetic properties of the individual enzymes involved. The system is able to exhibit alternative stable stationary states for one set of experimental conditions (bistability) originating mainly from the allosteric character of the phosphofructokinase. From a functional point of view, these states are either ATP-generating or ATP-consuming. Theoretically, the appearance of alternate steady states gives rise to hysteretic behavior of the system. In fact, transitions between alternate ATP generating stationary states as well as between ATP-generating and ATP-consuming steady states were observed experimentally.

Adenosine Triphosphate↗
PubMed1981

Self-stabilization of the energy charge in a reconstituted enzyme system containing phosphofructokinase.

The self-stabilization of the energy charge and of ATP was investigated in an open reconstituted enzyme system containing phosphofructokinase, pyruvate kinase, adenylate kinase, and glucose-6-phosphate isomerase. The experiments were performed in a stirred flow-through reactor containing gel-entrapped enzymes. The dynamics of the system were analyzed theoretically by a model based on the kinetic properties of the individual enzymes. The energy charge was identified as one of the essential variables of the system. According to the theoretical prediction, homoeostasis of the energy charge was observed experimentally when either the maximal activity of phosphofructokinase, the energy charge of the influx solution of the flow rate through the reaction chamber was varied. It is shown that the efficiency of stabilization of the energy charge is related to the occurrence of alternative stationary states.

Adenylate Kinase↗
PubMed1979

Kinetic modelling of yeast phosphofructokinase.

Phosphofructokinase from baker's yeast (Saccharomyces cerevisiae) is an octameric enzyme which exhibits complex allosteric behaviour. In contrast to mammalian phosphofructokinase, the enzyme does not show association-dissociation behaviour. A systematic kinetic investigation at pH 7.2 in dependence on the substrates, fructose 6-phosphate and ATP as well as on the effectors AMP and ADP is presented. The results are interpreted in terms of a structure oriented theoretical model. Because the two state model of Monod, Wyman and Changeux proved to be insufficient for interpretation of the experimental data, it was extended to a four state model in which the basic conformations R and T of the enzyme are split into subconformations R1 and R2 as well as T1 and T2, respectively. It is assumed that fructose 6-phosphate and the adenine nucleotides influence different allosteric equilibria. The model permits a precise quantitative description of the experimental data.

Adenosine Diphosphate↗
PubMed1979

Non-linear dynamic phenomena in open reconstituted enzyme systems.

The dynamic pattern of an open reconstituted in-vitro enzyme system containing phosphofructokinase, pyruvate kinase and adenylate kinase has been investigated. The approach is experimentally based on a stirred flow-through reactor. Stationary concentrations of phosphofructokinase and pyruvate kinase are maintained by entrapment in polyacrylamide gel particles. The results fit to a theoretical model based on the initial kinetic responses of the enzymes involved. An S-shaped steady state input characteristic for fructose 6-phosphate has been experimentally obtained.

Adenosine Triphosphate↗
PubMed1978

Kinetic investigation of the interaction of cibacron blue F3G-A with phosphofructokinase from yeast.

Yeast phosphofructokinase is strongly inhibited by Cibacron Blue F3G-A. The inhibition is competitive in respect to the phosphate donor. Fructose 6-phosphate and ATP are able to abolish the dye-inhibition. Replacement of the strong inhibitor ATP by ITP as phosphate donor gives qualitatively analogous effects. The influence of Cibacron Blue F3G-A on the kinetic pattern of yeast phosphofructokinase can be described in terms of the kinetic model of Freyer et al. [8] if one assumes that the dye binds to the ATP-binding sites in a competitive manner.

Anthracenes↗
PubMed1978

Association behaviour of human erythrocyte phosphofructokinase. Dependence of molecular weight on enzyme concentration as analyzed by frontal gel chromatography.

Self-association of human erythrocyte phosphofructokinase has been studied at pH 8.0 and at 4 degrees C in the presence of 2 mM fructose 6-phosphate by means of frontal gel chromatography. Under these conditions the basic associating catalytically active species is the tetramer of the enzyme with a molecular weight of about 330000, the monomers of which having a molecular weight of 83000 as determined by sodium dodecyl sulphate electrophoresis. The experimental data have been compared with various models describing the enzyme association. The mode of association can sufficiently be described by assuming a weakly negative cooperative process in which the association constant of the nucleation step (association of two tetramers to an octamer) is larger than that of the following propagation steps. The geometry of association appears to be approximately spherical.

Chromatography, Gel↗
PubMed1978

Dynamic properties of in vitro enzyme systems containing phosphofructokinase.

The dynamic properties of a series of in vitro reaction systems with increasing complexity and containing phosphofructokinase as central enzyme have been investigated. An experimental strategy and a principal mathematical treatment was elaborated to search for the minimum requirements with respect to the enzyme composition of a reaction system for generating limit cycle behaviour. As a criterion, such models have been developed which permit experimental realization by application of a specially designed flow-through equipment. In addition to phosphofructokinase, the following enzymes have been stepwise included into the reaction systems composing the Models 1 through 6: pyruvate kinase, adenylate kinase, hexokinase, and glucose 6-phosphate isomerase. It turned out that only a minimum dynamic system containing phosphofructokinase and pyruvate kinase as well as excesses of adenylate kinase and glucose 6-phosphate isomerase for maintaining equilibrium conditions between the respective reacting species, acquires the property of limit cycle behaviour and, hence, to generate sustained self-oscillations. The approach permits to compute the region of the experimentally variable parameters (influx rates of fructose 6-phosphate and ATP, maximum rate of pyruvate kianse) for which self-oscillatory behaviour can be predicted.

Adenylate Kinase↗