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B N Kholodenko

Publications and source records attributed to B N Kholodenko.

At least 55 records · Page 3Linked to original sources
PubMed1994

Rate limitation within a single enzyme is directly related to enzyme intermediate levels.

The extents to which different rate constants limit the steady-state rate of an isolated enzyme can be quantified as the control coefficients of those constants and elemental steps. We have found that the sum of the control coefficients of rate constants characterising unidirectional rates depleting a particular enzyme intermediate is equal to the concentration of that enzyme intermediate as a fraction of the total enzyme concentration. Together with simple measurements this powerful relation may be used (i) to estimate certain enzyme intermediate levels, in particular the free enzyme concentration, and (ii) to estimate the control coefficients of rate constants and steps.

Enzymes↗
PubMed1994

Getting to the inside of cells using metabolic control analysis.

Metabolic control analysis can relate control properties of an intact system to kinetic properties (elasticity coefficients) of the enzymes within that system. The method formulating the former as matrix inverse of the latter is elaborated here for the general case and founded in standard metabolic control theory. Then a method is developed that accomplishes the reverse: it is shown that a matrix containing all elasticity coefficients and information concerning the pathway structure equals the inverse of a matrix containing flux and concentration control coefficients. As a consequence, by measuring the control properties of an intact system, one is able to deduce its in situ pathway structure and enzyme kinetic properties: This solves the ever-present question of whether the kinetic properties of enzymes in their isolated state differ from those under the conditions prevailing in the cell.

Cells↗
PubMed1994

How to determine control of growth rate in a chemostat. Using metabolic control analysis to resolve the paradox.

The chemostat makes it possible to study microbial physiology at steady state. However, because growth rate in a chemostat is set by the experimenter, it seems impossible to employ the chemostat to study the control of microbial growth by processes within the microorganism. In this paper we show how, paradoxically, one can determine control of growth rate, of growth yield and of other fluxes in a chemostat. We develop metabolic control analysis for the chemostat. This analysis does not depend on the particular way in which specific growth rate varies with the concentration of the growth limiting substrate.

Bacteria↗
PubMed1993

Dramatic changes in control properties that accompany channelling and metabolite sequestration.

A simple summation theorem describes the control of fluxes in 'ideal' metabolic pathways. This paper shows how this theorem and the control properties of a pathway change when direct transfer of intermediates and/or sequestration of metabolites involved in moiety conservations (by enzymes present at high concentrations) take place. The derived generalized summation theorem quantifies the extent to which metabolite sequestration decreases and direct metabolite transfer can increase the control exerted by enzymes on the flux. The implications of metabolite channelling for the control of fluxes are discussed quantitatively.

Enzymes↗
PubMed1993

Metabolic channelling and control of the flux.

Metabolic control theory is extended to include channelled metabolism in general. A simple relationship between the flux control by the enzymes and the degree of metabolite channelling is derived. This relationship suggests experiments in which modulation of gene expression allows one to quantify channelling.

Enzymes↗
PubMed1993

'Channelled' pathways can be more sensitive to specific regulatory signals.

In 'simple' metabolic pathways the response to an external signal is readily described in terms of the effect of the signal on its receptor enzyme and the control exerted by that enzyme. We show here that in the response of 'channelled' pathways to such a signal, additional terms appear that reflect the direct enzyme-enzyme interactions. They tend to enhance the responsiveness of the pathway. The normalized value of the response is called the signal transduction coefficient. We show that in channelled pathways these coefficients are usually larger than in corresponding non-channelled (simple) pathways.

Enzymes↗
PubMed1993

The sum of the control coefficients of all enzymes on the flux through a group-transfer pathway can be as high as two.

In simple metabolic pathways the control exerted by enzyme concentrations on the pathway flux adds up to one when the control is quantified in terms of control coefficients. In this paper we demonstrate that this classical summation theorem has to be modified in pathways where the enzymes participate by transferring a group between each other. We derive the corresponding new control theorem and show how it is consistent with standard metabolic control analysis. In group-transfer pathways lacking enzyme complexes, the sum of the flux control by enzyme concentrations and by the donor and acceptor couples of the pathway, equals two. In group-transfer pathways with enzyme-enzyme interactions the flux control by the dissociation rate constants of the enzyme-enzyme complexes must be added to obtain this sum of two. In all cases, the sum of the controls by all reaction activities remains one. Both by using the new theorem and by numerical simulations, we then demonstrate that, in group-transfer pathways with or without enzyme interactions, the sum of the control of enzymes on the pathway flux is higher than one and can reach a value of two. The total control of all enzymes on the concentration of any intermediate either with or without the transferred group can be equal to one, rather than to the zero found in the classical case. Examples of group-transfer pathways are the bacterial phosphoenolpyruvate:sugar phosphotransferase system, the main pathway for uptake of sugars in Enterobacteriaceae, and the electron-transfer chain in free-energy transducing membranes.

Enzymes↗
PubMed1993

Kinetic models of coupling between H+ and Na(+)-translocation and ATP synthesis/hydrolysis by F0F1-ATPases: can a cell utilize both delta mu H+ and delta mu Na+ for ATP synthesis under in vivo conditions using the same enzyme?

Kinetic models of the F0F1-ATPase able to transport H+ or/and Na+ ions are proposed. It is assumed that (i) H+ and Na+ compete for the same binding sites, (ii) ion translocation through F0 is coupled to the rate-limiting step of the F1-catalyzed reaction. The main characteristics of the dependences of ATP synthesis and hydrolysis rates on delta psi, delta pH, and delta pNa are predicted for various versions of the coupling model. The mechanism of the switchover from delta mu H(+)-dependent synthesis to the delta mu Na(+)-dependent one is demonstrated. It is shown that even with a drastic drop in delta mu H+, ATP hydrolysis by the proton mode of catalysis can be effectively inhibited by delta psi and delta pNa. The results obtained strongly support the possibility that the same F0F1-ATPase in bacterial cells can utilize both delta muH+ and delta muNa+ for ATP synthesis under in vivo conditions.

Adenosine Triphosphate↗
PubMed1992

Control of the metabolic flux in a system with high enzyme concentrations and moiety-conserved cycles. The sum of the flux control coefficients can drop significantly below unity.

In a number of metabolic pathways enzyme concentrations are comparable to those of substrates. Recently it has been shown that many statements of the 'classical' metabolic control theory are violated if such a system contains a moiety-conserved cycle. For arbitrary pathways we have found: (a) the equation connecting coefficients CEiJ (obtained by varying the Ei concentration) and CviJ (obtained by varying the kicat), and (b) modified summation equations. The sum of the enzyme control coefficients (equal to unity under the 'classical' theory) appears always to be below unity in the systems considered. The relationships revealed were illustrated by a numerical example where the sum of coefficients CEiJ reached negative values. A method for experimental measurements of the above coefficients is proposed.

Enzymes↗
PubMed1991

[Regulation of the heart mitochondrial respiration rate. Comparison of oxidation of succinate and NAD-dependent substrates].

Regulation of respiration at all rates between State 4 and State 3 was studied in heart mitochondria oxidizing FAD- and NAD-dependent substrates (succinate, pyruvate + + malate and palmitoylcarnitine). The creatine phosphokinase ADP-regenerating system was used which allows to fix the concentrations of extramitochondrial adenine nucleotides in such a way that the rate of respiration is controlled by mitochondrial processes alone. It was shown that respiration is controlled by delta mu(H+)-utilizing system within the respiration rate interval from State 4 till 70-80% of the maximal rate in State 3 (corresponding to physiological rates) both for NAD- and FAD-dependent substrates. The main step in the control of respiration near State 4 is proton leakage through the inner mitochondrial membrane, whereas in all the other parts of the mentioned interval this role is assigned to the adenine nucleotide translocator (ANT). The control coefficient for ANT is higher, while that of proton leakage is lower at the same relative rates of respiration with NAD-dependent substrates compared with succinate. These differences were found to be related to much higher values of the membrane potential generated at the same relative rates of succinate oxidation in comparison with the case with pyruvate + + malate. The contribution of delta mu(H+)-utilizing system to respiration control sharply decreases, whereas that of the delta mu(H+)-generating system increases at maximal rates of respiration near State 3. This phenomenon in more characteristic of succinate. In this case the control coefficient of ANT drops to zero, while that of succinate dehydrogenase rises to 0.7.

Adenine Nucleotides↗
PubMed1989

[The role of long-chain acyl-CoA in the disturbances of oxidative phosphorylation in the myocardium].

The effect of intramitochondrial acyl-CoA on the respiration of rabbit heart mitochondria in different metabolic states was studied. Acyl-CoA inhibited O2 consumption by 11% in State 4 and by 6% in State 3. However, the effect of acyl-CoA was more pronounced (20%) in the intermediate state of respiration between State 4 and State 3. The data obtained suggest that acyl-CoA can regulate oxidative phosphorylation in heart mitochondria in vivo.

Acyl Coenzyme A↗
PubMed1988

How do external parameters control fluxes and concentrations of metabolites? An additional relationship in the theory of metabolic control.

The flux through a metabolic pathway can be controlled by external signals from the environment. These signals are formally described as changes in external parameters, such as concentrations of external metabolites (substrates or effectors) or physical parameters, e.g. temperature, pH, ionic strength. It was proved that the response coefficient of the flux (or of the concentration) to a change in an external parameter is the weighted average of external elasticities of pathway enzymes towards this parameter; weight factors are the control coefficients of corresponding enzymes. As compared with the previously known relationships these ones are applicable to the more common case of parameters acting on more than one enzyme. Along with other applications, the use of the obtained relationships for control analysis of moiety-conserved cycles is considered.

Adenosine Diphosphate↗
PubMed1988

[The role of adenine nucleotide translocator in the regulation of oxidative phosphorylation in heart mitochondria].

The regulatory role of adenine nucleotide translocase in oxidative phosphorylation was determined by titration of respiration of isolated rabbit heart mitochondria with carboxyatractyloside in the creatine phosphokinase ADP-regenerating system, which is not rate-limiting. It was found that the respiration rate is not controlled by adenine nucleotide translocase in states 3 and 4. Within the physiological region of respiration (30-70% of the maximal rate), the control coefficient for ADP/ATP translocase is 0.62-0.75. Thus, translocase plays a key role in the regulation of oxidative phosphorylation.

Animals↗
PubMed1984

Control of mitochondrial oxidative phosphorylation.

The objective of this investigation is to analyze the two following problems of the regulation of mitochondrial oxidative phosphorylation: what is the extramitochondrial parameter that controls ATP production according to the cytoplasmic demands and how the control is distributed between various mitochondrial enzymes. On the basis of the data of Groen et al. (1982) it is shown that as the respiration rates ranged over 30-50% of the maximum (i.e. within the physiological region) the contribution of the adenine nucleotide translocator to the control of the ATP flux is no less than 90%, referring to the total contribution of all mitochondrial enzymes as 100%. Founding on the key role of the adenine nucleotide translocator it has been concluded that besides the extramitochondrial [ATP]/[ADP] ratio the absolute ADP concentration is another extramitochondrial signal controlling significantly the rate of oxidative phosphorylation.

Adenosine Diphosphate↗
PubMed1982

Dynamic stability of steady states and static stabilization in unbranched metabolic pathways.

The paper is concerned with the conditions of dynamic (asymptotic) stability of steady states in unbranched metabolic pathways. The stationary flux in such pathways is generally determined by the concentration of the end product due to the effector action of this product on the reactions proceeding in its synthetic pathway. The delay in feedback circuits causes violation of dynamic stability at large static stabilization factors. A methods permitting analytic estimation of the critical stabilization factor is suggested. Sufficient and necessary conditions for asymptotic stability of the steady state in the general case of the pathway with a single feedback loop have been established. Mechanisms for maintenance of the steady state asymptotic stability at large static stabilization factors are studied. It has been shown that the range of dynamic stability can be widened greatly, if the pathway contains one or two reactions (but not more) of relatively small effective rate constants. Short strong negative feedback is also found to extend considerably the range of dynamic stability of the pathway. The feedback is more effective if it acts on the reaction with small effective rate constant.

Feedback↗
PubMed1981

Regulation of glycolysis in human erythrocytes. The mechanism of ATP concentration stabilization.

The mathematical modelling of human erythrocyte energy metabolism has shown that stabilization of ATP concentration can be achieved if the curve representing the relation between glycolysis rate and ATP concentration (glycolysis characteristic) is bell-shaped with steeply descending part at physiologically normal ATP concentration. The glycolysis characteristic of human erythrocytes has been obtained experimentally. In erythrocytes of different donors the glycolysis characteristics are greatly different quantitatively, but have qualitatively similar bel-like shape with steeply descending part at physiologically normal ATP concentration. This characteristics can be made coincident for all donors if they are plotted in relative units taking for 100% the physiologically normal values of glycolysis rate and ATP for every individual donor. The coincidence of the normalized erythrocyte glycolysis characteristics for different donors can be achieved in the mathematical model of erythrocyte energy metabolism under the assumption that the phosphofructokinase rate depends effectively on the relation of ATP to adenylate pool and the total erythrocyte ATPase is strongly inhibited by AMP.

Adenosine Triphosphate↗
PubMedDate not supplied

Control theory of metabolic channelling.

Various factors appear to control muscle energetics, often in conjunction. This calls for a quantitative approach of the type provided by Metabolic Control Analysis for intermediary metabolism and mitochondrial oxidative phosphorylation. To the extent that direct transfer of high energy phosphates and spatial organization plays a role in muscle energetics however, the standard Metabolic Control Theory does not apply, neither do its theorems regarding control. This chapter develops the Control Theory that does apply to the muscle system. It shows that direct transfer of high energy phosphates bestows a system with enhanced control: the sum of the control exerted by the participating enzymes on the flux of free energy form the mitochondrial matrix to the actinomyosin may well exceed the 100% mandatory for ideal metabolic pathways. It is also shown how sequestration of high energy phosphates may allow for negative control on pathway flux. The new control theory gives methods functionally to diagnose the extent to which channelling and metabolite sequestration occur.

Animals↗