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

1987 ◽  
Vol 245 (3) ◽  
pp. 935-935
Keyword(s):  
Rat Heart ◽  
Tricarboxylic Acid Cycle ◽  
Tricarboxylic Acid ◽  
Pool Size ◽  
Acid Cycle ◽  
Perfused Rat Heart ◽  
Tricarboxylic Acid Cycle Intermediates

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.

scholarly journals The conversion of alanine into glutamine in guinea-pig renal cortex. Essential role of pyruvate carboxylase

1981 ◽  
Vol 200 (1) ◽  
pp. 27-33 ◽  
Author(s):  
M Forissier ◽  
G Baverel
Keyword(s):  
Glutamine Synthetase ◽  
Guinea Pig ◽  
Pyruvate Carboxylase ◽  
Tricarboxylic Acid Cycle ◽  
Tricarboxylic Acid ◽  
Kidney Cortex ◽  
Acid Cycle ◽  
Ammonia Release ◽  
Tricarboxylic Acid Cycle Intermediates

1. The metabolism of L-alanine was studied in isolated guinea-pig kidney-cortex tubules. 2. In contrast with previous conclusions of Krebs [(1935) Biochem. J. 29, 1951-1969], glutamine was found to be the main carbon and nitrogenous product of the metabolism of alanine (at 1 and 5 mM). Glutamate and ammonia were only minor products. 3. At neither concentration of alanine was there accumulation of glucose, glycogen, pyruvate, lactate, aspartate or tricarboxylic acid-cycle intermediates. 4. Carbon-balance calculations and the release of 14CO2 from [U-14C]alanine indicate that oxidation of the alanine carbon skeleton occurred at both substrate concentrations. 5. A pathway involving alanine aminotransferase, glutamate dehydrogenase, glutamine synthetase, pyruvate dehydrogenase, pyruvate carboxylase and enzymes of the tricarboxylic acid cycle is proposed for the conversion of alanine into glutamine. 6. Strong evidence for this pathway was obtained by: (i) suppressing alanine removal by amino-oxyacetate, and inhibitor of transaminases, (ii) measuring the release of 14CO2 from [1-14C]alanine, (iii) the use of L-methionine DL-sulphoximine, an inhibitor of glutamine synthetase, which induced a large increase in ammonia release from alanine, and (iv) the use of fluoroacetate, an inhibitor of aconitase, which inhibited glutamine synthesis with concomitant accumulation of citrate from alanine. 7. In this pathway, the central role of pyruvate carboxylase, which explains the discrepancy between our results and those of Krebs (1935), was also demonstrated.

scholarly journals Metabolism of pent-4-enoate in rat heart. Reduction of the double bond

1981 ◽  
Vol 194 (2) ◽  
pp. 427-432 ◽  
Author(s):  
J K Hiltunen ◽  
E J Davis
Keyword(s):  
Double Bond ◽  
Rat Heart ◽  
No Reduction ◽  
Tricarboxylic Acid Cycle ◽  
Liver Mitochondria ◽  
Tricarboxylic Acid ◽  
Beta Oxidation ◽  
Initial Oxidation ◽  
Acid Cycle ◽  
Tricarboxylic Acid Cycle Intermediates

1. Soluble extracts from rat heart and liver mitochondria were used to evaluate the early steps in the conversion of pent-4-enoyl-CoA into tricarboxylic acid-cycle intermediates. Hitherto the unresolved problem was the reduction of the double bond of pent-4-enoate. 2. Soluble extracts from heart mitochondria reduced pent-4-enoyl-CoA and penta-2,4-dienoyl-CoA in the presence of NADPH at rates (nmol/min per mg of protein) of 0.9 +/- 0.1 and 132 +/- 8 and from the liver mitochondria at the rates of 1.9 +/- 0.2 and 52 +/- 6 respectively. No reduction of acryloyl-CoA was found. 3. We show that primarily the double bond in position 4, not in position 2, of penta-2,4-dienoyl-CoA is reduced. 4. It is concluded that the principal metabolic pathway of penta-4-enoate is reduction of the double bond in position 4 after an initial oxidation of penta-2,4-dienoyl-CoA. The pent-2-enoyl-CoA thus formed can be further metabolized by the usual enzymes of beta-oxidation, and by the further metabolism of propionyl-CoA to tricarboxylic acid-cycle intermediates.

scholarly journals Role of pyruvate carboxylation in the energy-linked regulation of pool sizes of tricarboxylic acid-cycle intermediates in the myocardium

1982 ◽  
Vol 208 (3) ◽  
pp. 577-581 ◽  
Author(s):  
K J Peuhkurinen ◽  
E M Nuutinen ◽  
E P Pietiläinen ◽  
J K Hiltunen ◽  
I E Hassinen
Keyword(s):  
Tricarboxylic Acid Cycle ◽  
Specific Radioactivity ◽  
Tricarboxylic Acid ◽  
Acid Cycle ◽  
Metabolite Pool ◽  
Label Incorporation ◽  
Tricarboxylic Acid Cycle Intermediates ◽  
Pool Sizes

The increase in the metabolite pool size of the tricarboxylic acid cycle in the isolated perfused rat heart after a decrease in the ATP consumption by KCl-induced arrest was used to study the anaplerotic mechanisms. During net anaplerosis the label incorporation into the tricarboxylic acid-cycle intermediates from [1-14C]pyruvate increased and occurred mainly by pathways not involving prior release of the label to CO2. A method for determination of the specific radioactivity of mitochondrial pyruvate was devised, and the results corroborated the notion that tissue alanine can be used as an indicator of the specific radioactivity of intracellular pyruvate.

scholarly journals Isolated rat heart mitochondria are able to metabolize pent-4-enoate to tricarboxylic acid-cycle intermediates

1980 ◽  
Vol 188 (3) ◽  
pp. 725-729 ◽  
Author(s):  
J K Hiltunen ◽  
R A Kauppinen ◽  
E M Nuutinen ◽  
K J Peuhkurinen ◽  
I E Hassinen
Keyword(s):  
Rat Heart ◽  
Tricarboxylic Acid Cycle ◽  
Tricarboxylic Acid ◽  
Isolated Rat Heart ◽  
Heart Mitochondria ◽  
Bicarbonate Buffer ◽  
Acid Cycle ◽  
Rat Heart Mitochondria ◽  
Tricarboxylic Acid Cycle Intermediates ◽  
Isolated Rat

The metabolism of four short-chain odd-number-carbon fatty acids, pentanoate, pent-4-enoate, propionate and acrylate, was studied in isolated rat heart mitochondria incubated in [14C]bicarbonate buffer. Under these conditions pentanoate was metabolized with a concomitant accumulation of malate and incorporation of 14CO2 into non-volatile compounds. The metabolism of propionate to tricarboxylic acid-cycle intermediates required the addition of ATP and oligomycin. After addition of a small amount of rotenone to the incubation medium, pent-4-enoate was metabolized with an increase in malate from less than 3 nmol/mg of protein to 34.0 +/- 1.5 nmol/mg in 40 min, during which time the amount of 14CO2 fixed in acid-stable compounds increased from 1.56 +/- 0.30 to 41.1 +/- 2.6 nmol/mg of protein. Acrylate was not metabolized under any of the conditions tested. The results show that cardiac mitochondria must have an enzyme system that is capable of reducing the double bond of either pent-4-enoate or its metabolities. That the metabolism of pent-4-enoate occurs through a reductive step and energy-dependent carboxylation is evident from the requirement for NAD+ reduction by partial inhibition of the mitochondrial respiratory chain and the presence of ATP and CO2. The results do not enable us to say whether the compound reduced is pent-4-enoyl-CoA or acryloyl-CoA.

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