Catalytic Facilitation and Membrane Bioenergetics

Kell, Douglas B.

doi:10.1016/b978-0-12-744040-8.50007-4

Cited by 32 publications

(14 citation statements)

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“…We based these equations on the assumption of ideal metabolism, such that the sum of the enzymes' flux control coefficients equals 1. Exceptions to this rule occur in cases of metabolic channelling (Kell & Westerhoff, 1985 ;Kholodenko & Westerhoff, 1993), in organized multienzyme systems, and group transfer (Van Dam e t al., 1993). The equations can be readily adjusted to these cases, but we have opted for simplicity here.…”

Section: Discussionmentioning

confidence: 99%

Protein burden in Zymomonas mobilis: negative flux and growth control due to overproduction of glycolytic enzymes

et al. 1995

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Increasing the expression of various glycolytic operons in Zymomonss mobilis caused a significant decrease rather than increase in the glycolytic flux and growth rate. Because the relative decrease depended on the amount of overexpressed protein, and was independent of which enzyme was overexpressed, we attributed it to a protein burden effect. More specifically, we examined if the decrease in glycolytic flux could be explained by a decreased concentration of other glycolytic enzymes (for which glucokinase was used as a marker enzyme). Using the summation theorem of metabolic control theory we predicted the extent of this protein burden effect. The predictions were in good agreement with the experimental observations. This suggests that the negative flux control is caused either by a simple competition of the overexpressed gene with the expression of all other genes or by simple dilution. Furthermore, we determined the implications of protein burden for the determination of the extent to which an enzyme limits a flux. We conclude that a protein burden can cause a significant underestimation of the flux control coefficient, especially if the enzyme under investigation is a highly expressed enzyme.Keywords : protein burden, Zymomonas mobilis, flux control, glycolysis, metabolic control analysis INTRODUCTIONAttempts to optimize metabolic processes, by overexpression of enzymes that are thought to be important in the determination of the overall rate of formation of the desired product, often lead to negative results (Schaaff e t al., 1989;Niederberger et a/., 1992). This can be due to:(1) an intuitive overestimation of the actual importance of the enzyme in the production process -a clear distinction should be made between essential and controlling enzymes (Jensen e t a/., 1993a, b); (2) a shift of control upon overexpression (De Hollander, 1994;Small & Kacser, 1993); or (3) additional effects caused by the overexpression (Bailey, 1993). In the first case a quan- titative metabolic control analysis should lead to the identification of the enzymes that do exert flux control (Kacser & Burns, 1973;Heinrich & Rapoport, 1974; Groen e t a/., 1982; Fell, 1992). In the second case combined overexpression of a group (module, Schuster e t al., 1993) of enzymes should help (Small & Kacser, 1993). In the third case, the unspecific negative effects can be divided into energetic effects (costs to produce extra protein) and competitive effects (if the proteinsynthesizing machinery is limiting). In this paper we will use the term protein burden for the negative effect on any part of cell function caused by the overexpression of a protein independent of its catalytic activity. In order to evaluate the importance of an enzyme for the control of any flux under study, it is important to distinguish specific negative effects of the catalytic activity from this 'nonspecific ' protein burden. Thus, a quantitative analysis of the negative effects of expression of recombinant protein is needed. The protein burden effect has been recognize...

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Section: Discussionmentioning

confidence: 99%

Protein burden in Zymomonas mobilis: negative flux and growth control due to overproduction of glycolytic enzymes

et al. 1995

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“…In non-ideal pathways the value of the former may depend not only on the pathway properties but also on the peculiarities of signal molecules, as emphasized by the argument % of the signal transduction coefficient. Here we will consider the simple case when the elasticities ~i s~, if k is an E/-dependent process (27) It follows from Eqs 26 and 27 that in this case the expression for the signal transduction coefficient will be following:…”

Section: ) [3]mentioning

confidence: 99%

“…Here, for signals satisfying Eq. (27) we compare the signal transduction coefficients of enzymes in ideal and channelled pathways, see Figs 4 and 5, respectively. It follows from the equations above (see , that for either enzyme the same additional term is present in the channelled pathway equating, C =LJJ, for the static channel (Fig.…”

Section: ) [3]mentioning

confidence: 99%

“…Membrane linked free energy transduction involving proton pumping [26] has also been proposed to involve direct transfer of protons or associated electric fields between adjacent proton pumps (see [27] as a review). Also in this case such transfer would normally occur in parallel to the generation of a proton electrochemical potential difference between the two aqueous bulk phases bordering the energy coupling membrane.…”

Section: Introductionmentioning

confidence: 99%

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Control theory of metabolic channelling

1995

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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 paper 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 from 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. (Mol Cell Biochem 143: 151-168, 1995)

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“…Hence the finding that the flux control coefficient of a certain enzyme is lower than 1, raises the question of where the rest of the control lies. Deviation of the sum of flux control coefficients of enzymes from 1 have been brought forward as evidence that a pathway may not be 'simple', but 'channelled' (Kell and Westerhoff, 1985 ;Westerhoff and Kell, 1988;Ovadi, 1991). For metabolic pathways with enzyme -enzyme interactions, control theory has since been extended Sauro and Kacser, 1990;Kholodenko, 1992).…”

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

Dam

Vlag

Kholodenko

et al. 1993

European Journal of Biochemistry

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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 grouptransfer 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 enzymeenzyme 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.

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Catalytic Facilitation and Membrane Bioenergetics

Cited by 32 publications

References 370 publications

Protein burden in Zymomonas mobilis: negative flux and growth control due to overproduction of glycolytic enzymes

Protein burden in Zymomonas mobilis: negative flux and growth control due to overproduction of glycolytic enzymes

Control theory of metabolic channelling

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

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