Flux control exerted by mitochondrial outer membrane carnitine palmitoyltransferase over β-oxidation, ketogenesis and tricarboxylic acid cycle activity in hepatocytes isolated from rats in different metabolic states

Drynan, Lesley; Quant, Patti A.; Zammit, Victor A.

doi:10.1042/bj3170791

Cited by 105 publications

(85 citation statements)

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“…It is to be emphasized that the sensitivity of L-CPTo to malonyl-CoA, as well as the K m for palmitoyl-CoA, are both modulated by physiological state [45][46][47][48] (but not in cardiac muscle [49]) and that these changes (i) can be mimicked by experimentally induced changes in the fluidity of the mitochondrial outer membrane in itro [50] and (ii) are correlated with changes in the molecular order of the lipids of outer membranes prepared from mitochondria isolated from livers of rats maintained under different physiological conditions [51]. It is inferred that protein-membrane interactions are likely to be important in determining the malonyl-CoA sensitivity of CPTo, and that they are likely to be due to interaction between the TM segments as well as between them and the annular membrane lipids [34].…”

Section: Malonyl-coa Action On Cptomentioning

confidence: 99%

The malonyl-CoA–long-chain acyl-CoA axis in the maintenance of mammalian cell function

Zammit

1999

Biochemical Journal

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Long-chain acyl-CoA esters have potent specific actions (e.g. on gene transcription, membrane trafficking) as well as non-specific ones (e.g. on phospholipid bilayers). They are synthesized on the cytosolic aspects of several intracellular membranes, to give rise to (a) cytosolic pool(s) to which a variety of enzymes and processes have access, including some localized in the nucleus. Their concentration in cells is highly regulated, interconversion with corresponding acylcarnitines being the most important mechanism involved. This reaction is catalysed by cytosol-accessible carnitine long-chain acyl (palmitoyl) transferase activities that are themselves located on multiple membrane systems. Regulation of these activities is through the inhibitory action of malonyl-CoA. Hence the existence of a potent malonyl-CoA-acyl-CoA axis through which many processes involved in the maintenance of mammalian cell function are regulated. The molecular, topographical and physiological interactions that make this possible are described and discussed.

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Section: Malonyl-coa Action On Cptomentioning

confidence: 99%

The malonyl-CoA–long-chain acyl-CoA axis in the maintenance of mammalian cell function

Zammit

1999

Biochemical Journal

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“…Therefore, we have shown previously that CPT I has a high flux control coefficient over total carbon flux in both mitochondria (Scheme 1a) and hepatocytes (Scheme 1b) isolated from adult rats [9,26] and over ketogenesis specifically in hepatocytes (Scheme 1c) from adult rats [26]. However, we have not formally reported flux control coefficients for CPT I over ketogenic flux specifically in either isolated mitochondria or hepatocytes (but see preliminary data [28]) from suckling rats.…”

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confidence: 83%

“…The acidified incubation medium was centrifuged and 0.4 mL of supernatant was used directly for assaying ketone bodies as 14 C-labelled acid-soluble products [26]. Control experiments showed fluxes to acid-soluble products and CO 2 to be linear during the 1 h incubation.…”

Section: Assays Of Ketone Bodies and Comentioning

confidence: 99%

“…The tangents (at zero inhibitor) [26] to the best-fit lines from data in Fig. 4 and the errors on the flux control coefficients were calculated using the SIMFIT package [37].…”

Section: Statistical Analysis Of Hepatocyte Datamentioning

confidence: 99%

“…The permeabilized cells were collected as a pellet and resuspended in 0.5 mL of KCl medium. Each 0.5 mL of ghost suspension was used to measure CPT I activity by total [ 3 H]palmitoylcarnitine accumulation using 320 mm l-[Me-3 H]carnitine (0.8 mCiḿ mol 21 ) and 135 mm palmitoyl-CoA (1% BSA) as substrates in 1 mL of assay cocktail [26].…”

Section: Permeabilization Of Hepatocytes and Assay Of Cpt I Activitymentioning

confidence: 99%

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Comparisons of flux control exerted by mitochondrial outer‐membrane carnitine palmitoyltransferase over ketogenesis in hepatocytes and mitochondria isolated from suckling or adult rats

New

Krauß

Elliott

et al. 1999

European Journal of Biochemistry

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The primary aim of this paper was to calculate and report flux control coefficients for mitochondrial outermembrane carnitine palmitoyltransferase (CPT I) over hepatic ketogenesis because its role in controlling this pathway during the neonatal period is of academic importance and immediate clinical relevance. Using hepatocytes isolated from suckling rats as our model system, we measured CPT I activity and carbon flux from palmitate to ketone bodies and to CO 2 in the absence and presence of a range of concentrations of etomoxir. (This is converted in situ to etomoxir-CoA which is a specific inhibitor of the enzyme.) From these data we calculated the individual flux control coefficients for CPT I over ketogenesis, CO 2 production and total carbon flux (0.51^0.03; ± 1.30^0.26; 0.55^0.07, respectively) and compared them with equivalent coefficients calculated by similar analyses [Drynan, L., Quant, P.A. & Zammit, V.A. (1996) Biochem. J. 317, 791±795] in hepatocytes isolated from adult rats (0.85^0.20; 0.23^0.06; 1.06^0.29). CPT I exerts significantly less control over ketogenesis in hepatocytes isolated from suckling rats than those from adult rats. In the suckling systems the flux control coefficients for CPT I over ketogenesis specifically and over total carbon flux (, 0.6) are not consistent with the enzyme being ratelimiting. Broadly similar results were obtained and conclusions drawn by reanalysis of previous data {from experiments in mitochondria isolated from suckling or adult rats [Krauss, S., Lascelles, C.V., Zammit, V.A. & Quant, P.A. (1996) Biochem. J. 319, 427±433]} using a different approach of control analysis, although it is not strictly valid to compare flux contol coefficients from different systems. Our overall conclusion is that flux control coefficients for CPT I over oxidative fluxes from palmitate (or palmitoyl-CoA) differ markedly according to (a) the metabolic state, (b) the stage of development, (c) the specific pathway studied and (d) the model system.Keywords: flux control coefficients; hepatocytes; mitochondria; carnitine palmitoyltransferase; ketogenesis.During the transient hypoglycaemia immediately after birth [1], when feeding is being established, ketone bodies derived from fat stores provide an alternative perinatal fuel to glucose. Subsequently, throughout the suckling period, hepatic ketogenesis generates the main circulating oxidative fuels for the brain and peripheral tissues and carbon precursors for essential myelination of the neonatal brain [2±5]. However, despite the central importance of this biochemical pathway to metabolic adaptation to extrauterine life, we do not currently understand precisely how its onset and development are regulated and controlled in healthy neonates [6]. Furthermore, it is clear that these mechanisms of regulation and control are impaired in certain clinical infants [7,8]. Without rigorous analyses we shall remain unable to understand and describe quantitatively how hepatic ketogenesis is regulated and controlled in both`normal' healthy infants ...

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Ketone Bodies

Morio

Wolfe

2015

Encyclopedia of Life Sciences

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Ketone bodies are water‐soluble equivalents of fatty acids. They can substitute for glucose in peripheral tissues, especially in the brain, when glucose becomes limited in physiological and pathological states. Recent findings demonstrate that they also act as signalling metabolites, thus participating in the organism adaptation to the environment, such as during fasting, calorie restriction or prolonged exercise. Diabetes is the most common pathological cause of elevated blood ketone bodies. Ketone bodies are produced in excess in response to low insulin levels and high levels of counterregulatory hormones, the result being the development of metabolic acidosis that is associated with serious health complications. Yet, ketogenic diets have been used for decades to increase ketone body synthesis for their neuroprotective properties as central signalling metabolites and as main energy‐providing substrate for the brain, in epilepsy and neurodegenerative diseases. Key Concepts Ketone bodies are key energy substrates and signalling molecules Ketone bodies participate in energy homeostasis Diabetic ketoacidosis is the most common pathological cause of elevated blood ketone bodies and is associated with serious health complications Ketone bodies are neuroprotective Ketone bodies offer promising perspectives in clinical therapy for certain metabolic diseases, neurodegenerative diseases and cancers

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Flux control exerted by mitochondrial outer membrane carnitine palmitoyltransferase over β-oxidation, ketogenesis and tricarboxylic acid cycle activity in hepatocytes isolated from rats in different metabolic states

Cited by 105 publications

References 32 publications

The malonyl-CoA–long-chain acyl-CoA axis in the maintenance of mammalian cell function

The malonyl-CoA–long-chain acyl-CoA axis in the maintenance of mammalian cell function

Comparisons of flux control exerted by mitochondrial outer‐membrane carnitine palmitoyltransferase over ketogenesis in hepatocytes and mitochondria isolated from suckling or adult rats

Ketone Bodies

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