6A long standing question… Is the control due to a single glycolytic enzyme?Is the control shared by many gl. enzymes?Does the control lie outside of glycolysis?Experimental evidence in several cases…If the control lies outside, the most sensible candidate is ATP consumption. The authors therefore sought ways to increase ATP consumption.
7Relevant papers:Koebmann BJ, Westerhoff HV, Snoep JL, Nilsson D, Jensen PR. (2002) The glycolytic flux in Escherichia coli is controlled by the demand for ATP. J. Bacteriol. 184:Koebmann BJ, Westerhoff HV, Snoep JL, Solem C, Pedersen MB, Nilsson D, Michelsen O, Jensen PR. (2002) The extent to which ATP demand controls the glycolytic flux depends strongly on the organism and conditions for growth. Mol Biol Rep. 29:41-5Koebmann BJ, Solem C, Pedersen MB, Nilsson D, Jensen PR (2002) Expression of Genes Encoding F1-ATPase Results in Uncoupling of Glycolysis from Biomass Production in Lactococcus lactis. Appl. Envir. Microb.68:4274–4282
8Plasmid for expression of F1-ATPase in E. coli Plasmid for expression of F1-ATPase in E. coli. The boxes indicate the specific genes or origin of replication. “CPX” indicates synthetic promoters.The A,G and D subunits of F1-ATPase code for the cytoplasmic F1 part of the (F1F0) H+-ATP synthase which possesses the catalytic site for ATP synthesis and/or hydrolysis. The combination of the α, β and γ subunits exerted the strongest ATPase activity
9ATP synthesis and proton translocation can be uncoupled (F1F0) H-ATP synthasePictures from Gruissem B&MBoPATP synthesis and proton translocation can be uncoupled
10Introduction of ATPase activity by overexpression of F1 genes Measuring in vitro ATPase activities:change in ATP concentration related to thetotal protein level is shown as a function oftime after the addition of cellular extracts.pCP44 (wt)Increasing ATPaseThe transformants have more ATPase activity when assayed in vitro
11Galactosidase activity is a good indicator for engineered ATPase activity Correlation between specific ATPase activity and specific -galactosidase activity.
12ATPADPATP/ADPATP+ADPIntroducing an ATPase activity has a measurable effect on ATP and ADP concentrationCorrelation between specific ATPase activity with ATP, ADP, ATPADP pools and [ATP]/[ADP] ratios.
13- Lower final cell density Increasing ATPasepCP44 (wt)- Slower growth- Lower final cell densityGrowth curves of E. coli BOE270 derivatives with F1-ATPase activities. Cell density (i.e., the OD450 value) is shown as a function of time of the cultures.
14- Faster glucose consumtption despite a reduced growth rate pCP44 (wt)Increasing ATPase- Faster glucose consumtption despite a reduced growth rateGlucose consumptions in E. coli BOE270 derivatives with F1-ATPase activities.
15Summarizing:The effect on ATP concentration (or growth rate) is not as big as the effect on Glucose consumption (glycolysis)or as the effect on biomass yield
16(ed. A. Cornish-Bowden), Universitat de València, Valencia, Spain. Anaerobic energy metabolism in yeast as a supply-demand system Jan-Hendrik S. Hofmeyr (1997)Capitolo del libro:New Beer in an Old Bottle: Eduard Buchner and the Growth of Biochemical Knowledge(ed. A. Cornish-Bowden), Universitat de València, Valencia, Spain.
17Metabolismo dell’ATPFig. 1. The main reactions involved in ATP production and consumption in a fermenting yeast cell. Abbreviations: HK: hexokinase; PFK: phosphofructokinase; PGK: phosphoglycerate kinase; PK; pyruvate kinase; AK: adenylate kinase. The reaction catalysed by adenylate kinase is depicted with a dotted line to indicate that it is considered to be in equilibrium, therefore carrying no net flux. The number associated with the adenylate kinase reaction indicates reaction stoichiometry. The block designated "Demand" symbolizes the set of non-glycolytic ATP-consuming reactions.
18Come possiamo indicare lo stato di carica del sistema ATP? Tra gli indicatori possibili ricordiamo:Energy Charge (ec)Adenilati carichi/Adenilati scarichi (c/u)Range 0 - 1Range 0 - +
19Usando come variabile la Energy charge (ec) invece che la concentrazione di ATP, il sistema si semplifica e può essere descritto come sistema di supply-demand di tipo ciclico (Fig. A)Usando come variabile c/u (o il rapporto molare ATP/ADP), il sistema si semplifica ulteriormente (B) e diventa un sistema di supply demand lineare.
20Ricadiamo quindi in un classico sistema Supply-demand trattato in precedenza
22Un controllo effettivo da parte del demand richiede che εdemand sia circa 20 volte più piccola di εsupplySiccome difficilmente εsupply può essere >4, allora εdemand dovrà essere <0.2
23Buona omeostasi di P, cioè piccole variazioni di (c/u) Se è quindi il demand ad avere il completo controllo sul flusso, l’entità della variazione di P (omeostasi di P) dipenderà solo da εsup“…the functions of flux and concentration control are mutually exclusive.”…the higher εsupply , the more effective the buffering of the c/u ratio.Cambiamenti nel demand cambiano il flusso, cambiamenti nel supply non cambiano il flusso…Buona omeostasi di P, cioè piccole variazioni di (c/u)
24Se introduciamo un leak (es. una ATPasi gratuita)
25Possiamo modulare vdemand e misurare ε e CJ Flusso in funzione di ATP/ADPLog(J) in funzione di Log(ATP/ADP)The relative glycolytic fluxes and growth ratesLogarithmic (scaled) relative fluxesDependence of glycolytic flux and growth rate on the [ATP]/[ADP] ratio, and calculation of elasticity and flux control coefficients.
26CJ del demand (calcolato in base a due diversi fitting della curva) ΔGp : cellular energy stateElasticità di supply e demand (growth) in funzione di ATP/ADPCJ del demand (calcolato in base a due diversi fitting della curva)The full line represents Ce2J1 based on the fitted polynomium for the relative growth rates whereas the dotted line represents Ce2J1 based on a linear fit for the relative growth rates
27Main conclusions (I)In wild type cells, catabolic reactions (glycolysis) have little flux controlIn other words, the glycolytic flux is controlled by the ATP demand (this ensures metabolite homeostasis)In cells with a high ATPase level, the control is more in the catabolic reactionsThis would account for the evidence (yeast, coli…) that glycolityc reactions have no flux control and explains the difference between the effect on growth rate and yield (ATP/ADP vs ATP hydrolysis)
28Altri esempi di ciclo futile: Due casi di enzimi glicolitici e gluconeogenetici che funzionano contemporaneamentePFK e PBPase; PyrK e PEPCKGlycolysis & Gluconeogenesis pathways are both spontaneous. If both pathways were simultaneously active within a cell it would constitute a "futile cycle" that would waste energy.Se i due enzimi sono attivi contemporaneamente, il risultato netto è l’idrolisi di ATP
29La velocità di crescita rallenta e la resa di cellule (g di cellule prodotte per g di glucosio) diminuisce.
30La velocità di produzione di EtOH aumenta del 22% [per il calcolo: 100 x (50.5 – 41.3) / 41.3 ]Purtroppo la maggiore resa non compensa il rallentamento della crescita.
31BrevettiPatent number: Filing date: May 22, 1997 Issue date: Oct 19, 19991) A method to increase the production of carbon dioxide by Saccharomyces cerevisiae … with a strain of Saccharomyces cerevisiae genetically modified so as to conduct at least two futile cycles in the anaerobic glycolytic pathway which results in increased …2) The method of claim 1 wherein said two futile cycles are effected by modifying said Saccharomyces cerevisiae to constitutively express the gene for fructose-1,6-biphosphatase and the gene for phosphoenolpyruvate carboxykinase.
32Same approach, different organism Lactobacillus lactis epresssing F1 ATPase activityCorrelation between specific -galactosidase activities and biomass yield for the F1-ATPase library.
33Correlation between specific -galactosidase activities and biomass yield for the F1-ATPase library. The specific –galactosidase activities and biomass yields were measured for overnight cultures of L. lactis strains grown in SA medium supplemented with 1.5 g of glucose per liter and 5 g of erythromycin per ml.
34Effect of uncoupled F1-ATPase on the intracellular energy level ATP+ADPATPATP/ADPADP
35Increasing ATPaseCultures were grown in batches without aeration at 30°C in SA medium supplemented with 1 g of glucose per liter
36Increasing ATPaseSteady-state consumption of glucose in L. lactis strains with uncoupled F1-ATPase during batch fermentation.
37The effect on growth rate (or ATP concentration) is as big as the effect on biomass yield No effect on glycolytic fluxLe misure fin qui descritte sono state fatte su cellule in crescita
38glycolytic flux increases up to its limit Effect of uncoupled F1-ATPase in nongrowing cellsglycolytic flux increases up to its limitIntracellular [ATP]/[ADP] ratios in resuspended cells
39Misure dalle cellule in crescita Dependence of glycolytic flux and growth rate on the [ATP]/[ADP] ratio and calculation of elasticity and flux control coefficients.The relative glycolytic fluxes and growth ratesLogarithmic (scaled) relative fluxesMisure dalle cellule in crescita
40Elasticities of glycolytic flux and growth rate Flux control by the demand forATP on the glycolytic fluxATP consumption has a very low control coefficient (<0.1) in growing Lactobacillus cells
42Conclusions (II)Glycolysis is close to its maximum capacity in growing Lactobacillus cellsATP demand is not limiting glycolytic fluxLarge difference between E. coli and Lactobacillus lactisThis can be interpreted in terms of the physiology (ATP yield: 2 vs 10, flux: 24 vs 7)In non growing Lactococcus cells, glycolysis is limited by ATP demand untill…
43Referenze addizionali Hofmeyr, J.S. Cornish-Bowden, A. (2000) Regulating the cellular economy of supply and demand. FEBS Lett., 476, ReviewHofmeyr (1997) "Anaerobic Energy Metabolism in Yeast as a Supply-Demand System, pp in New Beer in an Old Bottle: Eduard Buchner and the Growth of Biochemical Knowledge (ed. A. Cornish-Bowden), Universitat de València, Valencia, Spain.Kroukamp O, Rohwer JM, Hofmeyr JH, Snoep JL. (2002) Experimental supply-demand analysis of anaerobic yeast energy metabolism. Mol Biol Rep. 29:203-9.Hofmeyr JH, Kacser H, van der Merwe KJ.(1986) Metabolic control analysis of moiety-conserved cycles. Eur J Biochem. 155:631-41Oliver S. (2002) Demand managment in cells Nature 418:33-34 (Commentary)Moreno-Sánchez R, Saavedra E, Rodríguez-Enríquez S, Olín-Sandoval V. (2008) Metabolic Control Analysis: A Tool for Designing Strategies to Manipulate Metabolic Pathways J Biomed Biotechnol. 2008: