scholarly journals The analysis of rate limitation within enzymes: relations between flux control coefficients of rate constants and unidirectional rates, rate constants and thermodynamic parameters of single isolated enzymes

1994 ◽  
Vol 300 (1) ◽  
pp. 159-164 ◽  
Author(s):  
G C Brown ◽  
C E Cooper
Keyword(s):  
Thermodynamic Parameters ◽  
Rate Constant ◽  
Rate Constants ◽  
Enzyme Mechanism ◽  
Control Coefficient ◽  
Flux Control ◽  
Flux Control Coefficient ◽  
Flux Control Coefficients ◽  
Measuring Control ◽  
Control Coefficients

The extent to which a rate constant or step within an enzyme mechanism limits the net enzyme rate in a particular condition can be quantified as a flux control coefficient. We derive here a number of relations between the control coefficients and the unidirectional rates, rate constants, and thermodynamic parameters of the enzyme. These and other relations are used to suggest a number of methods for experimentally measuring control coefficients within enzymes.

Quantification of the control of carbohydrate catabolism in the tapeworm Hymenolepis diminuta

1993 ◽  
Vol 71 (7-8) ◽  
pp. 315-323 ◽  
Author(s):  
Wendy Y. Precious ◽  
John Barrett
Keyword(s):  
Phosphoenolpyruvate Carboxykinase ◽  
Glycogen Synthase ◽  
Hymenolepis Diminuta ◽  
Rate Equations ◽  
Control Analysis ◽  
Control Coefficient ◽  
Flux Control ◽  
Flux Control Coefficients ◽  
Carbohydrate Catabolism ◽  
Control Coefficients

The elasticities for the different steps of carbohydrate catabolism in the tapeworm Hymenolepis diminuta were estimated from perturbation experiments. These data were then used to calculate flux and metabolite control coefficients. Enzyme elasticities were also calculated from the rate equations and an independent estimate of the flux control coefficients for phosphoenolpyruvate carboxykinase was made by inhibitor titration. The values obtained for the flux control coefficients for carbohydrate breakdown in H. diminuta are consistent with how the pathway is thought to be controlled in vivo. A sensitivity analysis of the flux control coefficients of the important regulatory enzymes in the pathway shows that for hexokinase, phosphofructokinase, pyruvate kinase, and phosphoenolpyruvate carboxykinase there are three or four key elasticities which have a significant effect on the coefficient. For glycogen synthase, the major factor in determining the magnitude of the flux control coefficient is the relative flux through the branch.Key words: Hymenolepis diminuta, metabolic control analysis, control coefficient, enzyme elasticity.

scholarly journals Study of the flux and transition time control coefficient profiles in a metabolic system in vitro and the effect of an external stimulator

1989 ◽  
Vol 260 (3) ◽  
pp. 763-769 ◽  
Author(s):  
N V Torres ◽  
R Souto ◽  
E Meléndez-Hevia
Keyword(s):  
Transition Time ◽  
Rabbit Muscle ◽  
Control Coefficient ◽  
Metabolic System ◽  
Flux Control ◽  
Time Control ◽  
Coefficient Distribution ◽  
Flux Control Coefficients ◽  
Control Coefficients

Control of flux and transition time was investigated with a reconstructed rabbit muscle glycolytic system in vitro as an experimental model. The results show agreement with the summation property for the Flux Control Coefficients [Kacser & Burns (1973) Symp. Soc. Exp. Biol. 27, 65-104; Heinrich & Rapoport (1974) Eur. J. Biochem. 42, 89-95]. Control of flux is almost exclusively located at the hexokinase- and phosphofructokinase-catalysed steps, whereas control of transition time is distributed more evenly between the enzymes of the system. The summation value of the Transition Time Control Coefficients is near to -1, suggesting the existence of another Summation Theorem besides that already stated for Flux Control Coefficients. Finally, we study the effect of an external stimulator of the system (fructose 2,6-bisphosphate) on the Control Coefficient profiles. The effect appears to be greater on the Transition Time Control Coefficient distribution than on the Flux Control Coefficients.

Control analysis of photosynthetic sucrose synthesis: assignment of elasticity coefficients and flux-control coefficients to the cytosolic fructose 1,6-bisphosphatase and sucrose phosphate synthase

1989 ◽  
Vol 323 (1216) ◽  
pp. 327-338 ◽  
Keyword(s):  
Sucrose Phosphate Synthase ◽  
Control Analysis ◽  
Sucrose Synthesis ◽  
Flux Control ◽  
Fructose 1,6 Bisphosphatase ◽  
Flux Control Coefficients ◽  
Sucrose Phosphate ◽  
Control Coefficients ◽  
Phosphate Synthase

The use of elasticity coefficients and flux-control coefficients in a quantitative treatment of control is discussed, with photosynthetic sucrose synthesis as an example. Experimental values for elasticities for the cytosolic fructose 1,6-bisphosphatase and sucrose phosphate synthase are derived from their in vitro properties, and from an analysis of the in vivo relation between fluxes and metabolite levels. An empirical factor α , describing the response of the fructose 2,6-bisphosphate regulator cycle to fructose 6-phosphate is described, and an expression is derived relating α to the elasticities of the enzymes involved in this regulator cycle. The in vivo values for elasticities and α are then used in a modified form of the connectivity theorem to estimate the flux control coefficients of the cytosolic fructose 1,6-bisphosphatase and sucrose phosphate synthase during rapid photosynthetic sucrose synthesis.

scholarly journals Flux control coefficients determined by inhibitor titration: the design and analysis of experiments to minimize errors

1993 ◽  
Vol 296 (2) ◽  
pp. 423-433 ◽  
Author(s):  
J R Small
Keyword(s):  
Random Errors ◽  
Flux Control ◽  
Graph Method ◽  
Function Fitting ◽  
Fitting Method ◽  
Simple Extrapolation ◽  
Experimental Errors ◽  
Flux Control Coefficients ◽  
Fitted Function ◽  
Control Coefficients

This paper is a study into the effects of experimental error on the estimated values of flux control coefficients obtained using specific inhibitors. Two possible techniques for analysing the experimental data are compared: a simple extrapolation method (the so-called graph method) and a non-linear function fitting method. For these techniques, the sources of systematic errors are identified and the effects of systematic and random errors are quantified, using both statistical analysis and numerical computation. It is shown that the graph method is very sensitive to random errors and, under all conditions studied, that the fitting method, even under conditions where the assumptions underlying the fitted function do not hold, outperformed the graph method. Possible ways of designing experiments to minimize the effects of experimental errors are analysed and discussed.

scholarly journals Evidence that the flux control coefficient of the respiratory chain is high during gluconeogenesis from lactate in hepatocytes from starved rats. Implications for the hormonal control of gluconeogenesis and action of hypoglycaemic agents

1987 ◽  
Vol 247 (2) ◽  
pp. 449-457 ◽  
Author(s):  
H J Pryor ◽  
J E Smyth ◽  
P T Quinlan ◽  
A P Halestrap
Keyword(s):  
Fatty Acid ◽  
Fatty Acid Oxidation ◽  
Respiratory Chain ◽  
Glucose Production ◽  
Hormonal Control ◽  
Acid Oxidation ◽  
Control Coefficient ◽  
Atp Content ◽  
Flux Control ◽  
Flux Control Coefficient

1. Increasing concentrations of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), a mild respiratory-chain inhibitor [Halestrap (1987) Biochim. Biophys. Acta 927, 280-290], caused progressive inhibition of glucose production from lactate + pyruvate by hepatocytes from starved rats incubated in the presence or absence of oleate and gluconeogenic hormones. 2. No significant changes in tissue ATP content were observed, but there were concomitant decreases in ketone-body output and cytochrome c reduction and increases in NADH fluorescence and the ratios of [lactate]/[pyruvate] and [beta-hydroxybutyrate]/[acetoacetate]. 3. The inhibition by DCMU of palmitoylcarnitine oxidation by isolated liver mitochondria was used to calculate a flux control coefficient of the respiratory chain towards gluconeogenesis. In the presence of 1 mM-oleate, the calculated values were 0.61, 0.39 and 0.25 in the absence of hormone and in the presence of glucagon or phenylephrine respectively, consistent with activation of the respiratory chain in situ as previously suggested [Quinlan & Halestrap (1986) Biochem. J. 236, 789-800]. 4. Cytoplasmic oxaloacetate concentrations were shown to decrease under these conditions, implying inhibition of pyruvate carboxylase. 5. Inhibition of gluconeogenesis from fructose and dihydroxyacetone was also observed with DCMU and was accompanied by an increased output of lactate + pyruvate, suggesting that activation of pyruvate kinase was occurring. With the latter substrate, measurements of tissue ADP and ATP contents showed that DCMU caused a small fall in [ATP]/[ADP] ratio. 6. Two inhibitors of fatty acid oxidation, pent-4-enoate and 2-tetradecylglycidate, were shown to abolish and to decrease respectively the effects of hormones, but not valinomycin, on gluconeogenesis from lactate + pyruvate, without changing tissue ATP content. 7. It is concluded that the hormonal increase in mitochondrial matrix volume stimulates fatty acid oxidation and respiratory-chain activity, allowing stimulation of pyruvate carboxylation and thus gluconeogenesis to occur without major changes in [ATP]/[ADP] or [NADH]/[NAD+] ratios. 8. The high flux control coefficient of the respiratory chain towards gluconeogenesis may account for the hypoglycaemic effect of mild respiratory-chain inhibitors.

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