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The mechanism of palmitoyl-CoA inhibition of Ca2+ uptake in liver and heart mitochondria.

ABSTRACT: The mechanism by which palmitoyl-CoA inhibits Ca2+ uptake in liver and heart mitochondria was examined. At a given concentration of palmitoyl-CoA, the extent of inhibition is inversely related to the concentration of the respiratory substrate succinate. Palmitoyl-CoA inhibition of uncoupler-stimulated respiration and respiration stimulated by ionophore-A23187-induced Ca2+ cycling is also relieved by high succinate concentrations. These effects of palmitoyl-CoA and succinate concentration are distinct from the increase in inner-membrane permeability, which can be produced by palmitoyl-CoA and Ca2+ [Beatrice, Palmer & Pfeiffer (1980) J. Biol. Chem. 255, 8663-8671]. The apparent K0.5 of the mitochondrial Ca2+ pump is not altered by palmitoyl-CoA. No or negligible effects of palmitoyl-CoA on the Ca2+-uptake rate are observed when ascorbate replaces succinate as an energy source. These findings, together with the known activity of palmitoyl-CoA as a competitive inhibitor of the dicarboxylate carrier [Morel, Lauquin, Lunardi, Duszynski & Vignais (1974) FEBS Lett. 39, 133-138], indicate that palmitoyl-CoA inhibits energy-linked Ca2+ transport by limiting the rate of electron transport through limitation of succinate entry into the mitochondria rather than by directly inhibiting the Ca2+ carrier.

SUBMITTER: Beatrice MC

PROVIDER: S-EPMC1162718 | biostudies-other | 1981 Jan

REPOSITORIES: biostudies-other

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Diabetic mitochondria are resistant to palmitoyl CoA inhibition of respiration, which is detrimental during ischemia.

Project description:The bioactive lipid intermediate palmitoyl CoA (PCoA) can inhibit mitochondrial ADP/ATP transport, though the physiological relevance of this regulation remains unclear. We questioned whether myocardial ischemia provides a pathological setting in which PCoA regulation of ADP/ATP transport would be beneficial, and secondly, whether the chronically elevated lipid content within the diabetic heart could make mitochondria less sensitive to the effects of PCoA. PCoA acutely decreased ADP-stimulated state 3 respiration and increased the apparent Km for ADP twofold. The half maximal inhibitory concentration (IC50 ) of PCoA in control mitochondria was 22 µM. This inhibitory effect of PCoA on respiration was blunted in diabetic mitochondria, with no significant difference in the Km for ADP in the presence of PCoA, and an increase in the IC50 to 32 µM PCoA. The competitive inhibition by PCoA was localised to the phosphorylation apparatus, particularly the ADP/ATP carrier (AAC). During ischemia, the AAC imports ATP into the mitochondria, where it is hydrolysed by reversal of the ATP synthase, regenerating the membrane potential. Addition of PCoA dose-dependently prevented this wasteful ATP hydrolysis for membrane repolarisation during ischemia, however, this beneficial effect was blunted in diabetic mitochondria. Finally, using 31 P-magnetic resonance spectroscopy we demonstrated that diabetic hearts lose ATP more rapidly during ischemia, with a threefold higher ATP decay rate compared with control hearts. In conclusion, PCoA plays a role in protecting mitochondrial energetics during ischemia, by preventing wasteful ATP hydrolysis. However, this beneficial effect is blunted in diabetes, contributing to the impaired energy metabolism seen during myocardial ischemia in the diabetic heart.

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Hedgehog Acyltransferase Promotes Uptake of Palmitoyl-CoA across the Endoplasmic Reticulum Membrane.

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Diabetic mitochondria are resistant to palmitoyl CoA inhibition of respiration, which is detrimental during ischaemia

Project description:The bioactive lipid intermediate palmitoyl CoA (PCoA) can inhibit mitochondrial ADP/ATP transport, though the physiological relevance of this regulation remains unclear. We questioned whether myocardial ischaemia was a pathological setting in which PCoA regulation of ADP/ATP transport would be beneficial. Secondly, whether the chronically elevated lipid content within the diabetic heart would make the mitochondria less sensitive to the inhibitory effects of PCoA, with detrimental consequences during ischaemia. Palmitoyl CoA acutely decreased ADP-stimulated state 3 respiration, increasing the Km for ADP 2-fold. The half maximal inhibitory concentration (IC50) of PCoA in control mitochondria was 22 µM. This inhibitory effect of PCoA on respiration was blunted in the diabetic mitochondria, with no significant difference in the Km in the presence of PCoA, and the IC50 increased to 32 µM PCoA. The competitive inhibition by PCoA was localised to the phosphorylation apparatus, particularly the ADP/ATP carrier (AAC). During ischaemia, the AAC imports ATP into the mitochondria, where it is hydrolysed by reversal of the ATP synthase, to regenerate the membrane potential. Addition of PCoA dose-dependently prevented this wasteful ATP hydrolysis for membrane repolarisation during ischaemia. However, this beneficial effect was blunted in the diabetic mitochondria. Finally, using 31P-magnetic resonance spectroscopy we demonstrated that diabetic hearts lose ATP more rapidly during ischaemia, with a 3-fold higher ATP decay rate compared with control hearts. In conclusion, PCoA plays a role in protecting mitochondrial energetics during ischaemia, by preventing wasteful ATP hydrolysis. However, this beneficial effect is blunted in diabetes, contributing to the impaired energy metabolism during myocardial ischaemia.

2022-02-17 | PXD024500 | Pride

Pathways for Ca2+ efflux in heart and liver mitochondria.

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Transport of Ca2+ and Ca2+-Dependent Permeability Transition in the Liver and Heart Mitochondria of Rats with Different Tolerance to Acute Hypoxia.

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Carnitine acyltransferase activities in rat liver and heart measured with palmitoyl-CoA and octanoyl-CoA. Latency, effects of K+, bivalent metal ions and malonyl-CoA.

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Project description:The overt form of carnitine palmitoyltransferase (CPT1) in rat liver and heart mitochondria was inhibited by DL-2-bromopalmitoyl-CoA and bromoacetyl-CoA. S-Methanesulphonyl-CoA inhibited liver CPT1. The inhibitory potency of DL-2-bromopalmitoyl-CoA was 17 times greater with liver than with heart CPT1. Inhibition of CPT1 by DL-2-bromopalmitoyl-CoA was unaffected by 5,5'-dithiobis-(2-nitrobenzoic acid) or (in liver) by starvation. In experiments in which DL-2-bromopalmitoyl-CoA displaced [14C]malonyl-CoA bound to liver mitochondria, the KD (competing) was 25 times the IC50 for inhibition of CPT1 providing evidence that the malonyl-CoA-binding site is unlikely to be the same as the acyl-CoA substrate site. Bromoacetyl-CoA inhibition of CPT1 was more potent in heart than in liver mitochondria and was diminished by 5,5'-dithiobis-(2-nitrobenzoic acid) or (in liver) by starvation. Bromoacetyl-CoA displaced bound [14C]malonyl-CoA from heart and liver mitochondria. In heart mitochondria this displacement was competitive with malonyl-CoA and was considerably facilitated by L-carnitine. In liver mitochondria this synergism between carnitine and bromoacetyl-CoA was not observed. It is suggested that bromoacetyl-CoA interacts with the malonyl-CoA-binding site of CPT1. L-Carnitine also facilitated the displacement by DL-2-bromopalmitoyl-CoA of [14C]malonyl-CoA from heart, but not from liver, mitochondria. DL-2-Bromopalmitoyl-CoA and bromoacetyl-CoA also inhibited overt carnitine octanoyl-transferase in liver and heart mitochondria. These findings are discussed in relation to inter-tissue differences in (a) the response of CPT1 activity to various inhibitors and (b) the relationship between high-affinity malonyl-CoA-binding sites and those sites for binding of L-carnitine and acyl-CoA substrates.

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Effects of calmodulin antagonists on the active Ca2+ uptake by rat liver mitochondria.

Project description:The mechanism of Ca2+ transport by rat liver mitochondria was investigated with respect to the possible involvement of calmodulin in this process. We studied the action of exogenous calmodulin isolated from brain tissue on the Ca2+-transport system, as well as the effect of two types of calmodulin antagonists; the phenothiazine drugs trifluoperazine and chlorpromazine and the more specific substance compound 48/80. Our results show that Ca2+ transport by mitochondria and mitochondrial ATPase activity are insensitive to exogenous calmodulin, although they can be inhibited by the phenothiazines. Since no effect of compound 48/80 was observed, we believe that the phenothiazines act through a mechanism that does not involve calmodulin. This is in accord with our inability to locate significant quantities of calmodulin in mitochondria by radioimmunoassay analysis. Our results further show that trifluoperazine and chlorpromazine also inhibit the electron-carrier system of the respiratory chain, and this effect may mediate their inhibitory action on Ca2+ transport when it is energized by respiration instead of ATP hydrolysis.

| S-EPMC1152334 | biostudies-other

Nitration of tryptophan 372 in succinyl-CoA:3-ketoacid CoA transferase during aging in rat heart mitochondria.

Project description:The main objective of this study was to test the hypothesis that in vivo post-translational modifications in proteins, induced by the endogenously generated reactive oxygen and nitrogen molecules, can alter protein function and thereby have an effect on metabolic pathways during the aging process. Succinyl-CoA:3-ketoacid coenzyme A transferase (SCOT), the mitochondrial enzyme involved in the breakdown of ketone bodies in the extrahepatic tissues, was identified in rat heart to undergo age-associated increase in a novel, nitro-hydroxy, addition to tryptophan 372, located in close proximity ( approximately 10 A) of the enzyme active site. Between 4 and 24 months of age, the molar content of nitration was more than doubled while specific enzyme activity increased significantly. The amount of SCOT protein, however, remained unchanged. In vitro treatment of heart mitochondrial soluble proteins with relatively low concentrations of peroxynitrite enhanced the nitration as well as specific activity of SCOT. Results of this study identify tryptophan to be a specific target of nitration in vivo, for the first time. We hypothesize that increases in tryptophan nitration of SCOT and catalytic activity constitute a plausible mechanism for the age-related metabolic shift toward enhanced ketone body consumption as an alternative source of energy supply in the heart.

| S-EPMC2526316 | biostudies-literature

Reversible sensitization and desensitization of carnitine palmitoyltransferase I to inhibition by malonyl-CoA in isolated rat liver mitochondria. Significance for the mechanism of malonyl-CoA-induced sensitization.

Project description:Preincubation of rat liver mitochondria with 5,5'-dithiobis-(2-nitrobenzoic acid) (Nbs2) followed by removal of excess reagent by washing the mitochondria with 0.5 mM-reduced glutathione resulted in a desensitization of carnitine palmitoyltransferase (CPT) I activity to malonyl-CoA inhibition. The effect was not observed if mitochondria were washed with 0.5 mM-dithiothreitol. The desensitization effect of Nbs2 could be reversed by a second incubation in the presence of 8 microM-malonyl-CoA. In addition, malonyl-CoA, when present simultaneously with Nbs2, protected CPT I activity against the desensitization effect of the thiol-group reagent. These results suggest that malonyl-CoA exerts an effect on one or more thiol groups of the enzyme, and that this effect is related to the ability of the metabolite to sensitize CPT I to malonyl-CoA inhibition.

| S-EPMC1152351 | biostudies-other

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