Computer simulation of metabolism in pyruvate-perfused rat heart. II. Krebs cycle

1979 ◽  
Vol 237 (3) ◽  
pp. R159-R166 ◽  
Author(s):  
M. C. Kohn ◽  
M. J. Achs ◽  
D. Garfinkel
Keyword(s):  
Redox Potential ◽  
Rat Heart ◽  
Citrate Synthase ◽  
Tricarboxylic Acid Cycle ◽  
Krebs Cycle ◽  
Coordinated Control ◽  
Work Load ◽  
Metabolic Model ◽  
Tricarboxylic Acid ◽  
Perfused Rat Heart

A realistic metabolic model of the tricarboxylic acid cycle in the perfused rat heart was constructed to help explain the sequence of biochemical events regulating the metabolism of exogenous pyruvate following a large increase in work load. The unchelated Mg2+ level was the most important controlling factor. The resulting mixture of chelated and unchelated nucleotides and tribasic acids effected coordinated control of citrate synthase, aconitase, isocitrate dehydrogenase, succinyl CoA synthetase, fumarase, and nucleoside diphosphokinase, because Mg2+-chelates are generally substrates whereas unchelated species are inhibitors. Succinate dehydrogenase is largely controlled by the ubiquinone redox potential. The fluxes through alpha-ketoglutarate and malate dehydrogenases are largely dependent on thepyridine nucleotide redox potential, but the succinyl CoA-to-CoASH ratio strongly affects the former enzyme as well. The model predicts an accumulation of succinate during the transition to higher work output.

scholarly journals Tricarboxylic acid cycle flux and enzyme activities in the isolated working rat heart

1981 ◽  
Vol 200 (3) ◽  
pp. 701-703 ◽  
Author(s):  
G J Cooney ◽  
H Taegtmeyer ◽  
E A Newsholme
Keyword(s):  
Oxygen Consumption ◽  
Enzyme Activities ◽  
Rat Heart ◽  
Citrate Synthase ◽  
Tricarboxylic Acid Cycle ◽  
Work Load ◽  
Tricarboxylic Acid ◽  
Acid Cycle ◽  
Oxoglutarate Dehydrogenase ◽  
Working Rat Heart

Flux through the tricarboxylic acid cycle was calculated from oxygen consumption in hearts perfused near the physiological work load. Activities of citrate synthase, 2-oxoglutarate dehydrogenase and succinate dehydrogenase were measured in the same hearts. Only the activities of 2-oxoglutarate dehydrogenase correlated with calculated fluxes through the cycle.

scholarly journals Role of NADP+-linked malic enzymes as regulators of the pool size of tricarboxylic acid-cycle intermediates in the perfused rat heart

1987 ◽  
Vol 243 (3) ◽  
pp. 853-857 ◽  
Author(s):  
K E Sundqvist ◽  
J Heikkilä ◽  
I E Hassinen ◽  
J K Hiltunen
Keyword(s):  
Malic Enzyme ◽  
Rat Heart ◽  
Tricarboxylic Acid Cycle ◽  
Tricarboxylic Acid ◽  
Mass Action ◽  
Acid Cycle ◽  
Perfused Rat Heart ◽  
Order Of Magnitude ◽  
Propionate Oxidation ◽  
Tricarboxylic Acid Cycle Intermediates

Cytosolic and mitochondrial concentrations of malate, 2-oxoglutarate, isocitrate and pyruvate in the isolated perfused rat heart were measured by non-aqueous tissue fractionation, taking the NADP-linked isocitrate dehydrogenase as indicator reactions for the free [NADPH]/[NADP+] ratios. The mass-action ratios of NADP-linked malic enzymes (EC 1.1.1.40) were found to be on the side of pyruvate carboxylation by more than one order of magnitude in both the cytosolic and the mitochondrial spaces in hearts perfused with glucose, whereas during propionate perfusion this ratio approached the equilibrium constant (Keq.) of malic enzyme. The results consequently indicate that the NADP-linked malic enzymes cannot be responsible for the feed-out (cataplerotic) reactions from the tricarboxylic acid cycle which occur during glucose perfusion. Only when other anaplerotic fluxes into the cycle are high, as during propionate oxidation, which results in accumulation of tricarboxylic acid-cycle intermediates, is a steady state reached which allows efflux via the malic enzyme.

Saccharomyces cerevisiae contains two functional citrate synthase genes

1986 ◽  
Vol 6 (6) ◽  
pp. 1936-1942
Author(s):  
K S Kim ◽  
M S Rosenkrantz ◽  
L Guarente
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Carbon Source ◽  
Citrate Synthase ◽  
Tricarboxylic Acid Cycle ◽  
Nuclear Gene ◽  
Tricarboxylic Acid ◽  
Yeast Genome ◽  
Gene Encoding ◽  
Acid Cycle ◽  
Nonfermentable Carbon Source

The tricarboxylic acid cycle occurs within the mitochondria of the yeast Saccharomyces cerevisiae. A nuclear gene encoding the tricarboxylic acid cycle enzyme citrate synthase has previously been isolated (M. Suissa, K. Suda, and G. Schatz, EMBO J. 3:1773-1781, 1984) and is referred to here as CIT1. We report here the isolation, by an immunological method, of a second nuclear gene encoding citrate synthase (CIT2). Disruption of both genes in the yeast genome was necessary to produce classical citrate synthase-deficient phenotypes: glutamate auxotrophy and poor growth on rich medium containing lactate, a nonfermentable carbon source. Therefore, the citrate synthase produced from either gene was sufficient for these metabolic roles. Transcription of both genes was maximally repressed in medium containing both glucose and glutamate. However, transcription of CIT1 but not of CIT2 was derepressed in medium containing a nonfermentable carbon source. The significance of the presence of two genes encoding citrate synthase in S. cerevisiae is discussed.

scholarly journals Association of the malate dehydrogenase-citrate synthase metabolon is modulated by intermediates of the Krebs tricarboxylic acid cycle

2021 ◽  
Author(s):  
Joy Omini ◽  
Izabela Wojciechowska ◽  
Aleksandra Skirycz ◽  
Hideaki Moriyama ◽  
Toshihiro Obata
Keyword(s):  
Malate Dehydrogenase ◽  
Metabolic Flux ◽  
Citrate Synthase ◽  
Tricarboxylic Acid Cycle ◽  
Feedback Regulation ◽  
Dynamic Structure ◽  
Tca Cycle ◽  
Tricarboxylic Acid ◽  
Enzyme Complex ◽  
Acetyl Coa

Mitochondrial malate dehydrogenase (MDH)-citrate synthase (CS) multi-enzyme complex is a part of the Krebs tricarboxylic acid (TCA) cycle 'metabolon' which is enzyme machinery catalyzing sequential reactions without diffusion of reaction intermediates into a bulk matrix. This complex is assumed to be a dynamic structure involved in the regulation of the cycle by enhancing metabolic flux. Microscale Thermophoresis analysis of the porcine heart MDH-CS complex revealed that substrates of the MDH and CS reactions, NAD+ and acetyl-CoA, enhance complex association while products of the reactions, NADH and citrate, weaken the affinity of the complex. Oxaloacetate enhanced the interaction only when it was presented together with acetyl-CoA. Structural modeling using published CS structures suggested that the binding of these substrates can stabilize the closed format of CS which favors the MDH-CS association. Two other TCA cycle intermediates, ATP, and low pH also enhanced the association of the complex. These results suggest that dynamic formation of the MDH-CS multi-enzyme complex is modulated by metabolic factors responding to respiratory metabolism, and it may function in the feedback regulation of the cycle and adjacent metabolic pathways.

scholarly journals Tricarboxylic acid cycle and proton gradient in Pandoravirus massiliensis: Is it still a virus?

2020 ◽  
Author(s):  
Sarah Aherfi ◽  
Djamal Brahim Belhaouari ◽  
Lucile Pinault ◽  
Jean-Pierre Baudoin ◽  
Philippe Decloquement ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Isocitrate Dehydrogenase ◽  
Energy Production ◽  
Citrate Synthase ◽  
Tricarboxylic Acid Cycle ◽  
Tricarboxylic Acid ◽  
Proton Gradient ◽  
Giant Virus ◽  
Acid Cycle ◽  
Key Enzyme

ABSTRACTSince the discovery of Acanthamoeba polyphaga Mimivirus, the first giant virus of amoeba, the historical hallmarks defining a virus have been challenged. Giant virion sizes can reach up to 2.3 µm, making them visible by optical microscopy. They have large genomes of up to 2.5 Mb that encode proteins involved in the translation apparatus. Herein, we investigated possible energy production in Pandoravirus massiliensis, the largest of our giant virus collection. MitoTracker and TMRM mitochondrial membrane markers allowed for the detection of a membrane potential in virions that could be abolished by the use of the depolarizing agent CCCP. An attempt to identify enzymes involved in energy metabolism revealed that 8 predicted proteins of P. massiliensis exhibited low sequence identities with defined proteins involved in the universal tricarboxylic acid cycle (acetyl Co-A synthase; citrate synthase; aconitase; isocitrate dehydrogenase; α-ketoglutarate decarboxylase; succinate dehydrogenase; fumarase). All 8 viral predicted ORFs were transcribed together during viral replication, mainly at the end of the replication cycle. Two of these proteins were detected in mature viral particles by proteomics. The product of the ORF132, a predicted protein of P. massiliensis, cloned and expressed in Escherichia coli, provided a functional isocitrate dehydrogenase, a key enzyme of the tricarboxylic acid cycle, which converts isocitrate to α-ketoglutarate. We observed that membrane potential was enhanced by low concentrations of Acetyl-CoA, a regulator of the tricarboxylic acid cycle. Our findings show for the first time that energy production can occur in viruses, namely, pandoraviruses, and the involved enzymes are related to tricarboxylic acid cycle enzymes. The presence of a proton gradient in P. massiliensis coupled with the observation of genes of the tricarboxylic acid cycle make this virus a form a life for which it is legitimate to question ‘what is a virus?’.

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