Pyruvate dehydrogenase and the hormonal regulation of fat synthesis in mammalian tissues

Denton, Richard M.; Hughes, William A.

doi:10.1016/0020-711x(78)90113-1

Cited by 78 publications

(25 citation statements)

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“…Addition of insulin to this subcellular system caused a plasma membrane-mediated decrease in the phosphorylation of a mitochondrial protein, identified as the a subunit of pyruvate dehydrogenase [pyruvate:lipoamide oxidoreductase (decarboxylating and acceptor-acetylating), EC 1.2.4.1]. This effect was consistent with the proposed model of insulin action on pyruvate dehydrogenase in the intact cell (3,4). From these data, it was predicted that the activity of pyruvate dehydrogenase should be stimulated by the addition of insulin to the plasma membrane/mitochondria mixture.…”

supporting

confidence: 77%

Activation of pyruvate dehydrogenase by direct addition of insulin to an isolated plasma membrane/mitochondria mixture: Evidence for generation of insulin's second messenger in a subcellular system

Seals

Jarett

1980

Proc. Natl. Acad. Sci. U.S.A.

147

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The addition of insulin to a mixture of plasma membrane and mitochondrial fractions from rat adipocytes results in a decrease in the phosphorylation of a mitochondrial protein identified as the a subunit of pyruvate dehydrogenase [pyruvate:lipoamide oxidoreductase (decarboxylating and acceptor-acetylating), EC 1.2.4.11 (Seals, J. R., McDonald, J. M. & Jarett, L. (1979) J. BioL Chem. 254,[6991][6992][6993][6994][6995][6996]. This study confirms the prediction that a corresponding increase in pyruvate dehydrogenase activity can be effected by insulin treatment of this preparation. Incubation of the plasma membrane/mitochondria mixture with ATP inhibited pyruvate dehydrogenase activity as measured in a subsequent enzyme assay. The presence of insulin during this incubation with ATP resulted in a 24.5% stimulation of enzyme activity compared to incubation without insulin (n = 9, P < 0.001). The effect was specific for biologically active insulin and was insulin dose-dependent in the physiological range of insulin. Supermaximal doses of insulin produced reduced effects. An insulin effect of similar magnitude could also be observed when the plasma membrane/mitochondria mixture was incubated without ATP. Two insulin mimickers, concanavalin A and antibody to insulin receptor, stimulated pyruvate dehydrogenase by 30.4% (n = 6, P < 0.001) and 28.1% (n = 8, P < 0.001), respectively. Both of these agents also produced reduced effects at supermaximal concentrations. The effects of all three agents required plasma membranes and could not be produced by treatment of mitochondria alone. The results suggest that a mechanism common to all three agents is responsible for transmitting the stimulation from the plasma membrane to the mitochondrial components of the mixture.Analysis of the mechanism of insulin action on its target cells has been hindered by the complex interactions among metabolic and regulatory factors in the intact cell. However, insulin action has recently been demonstrated in a simplified subcellular system consisting of a mixture of purified plasma membrane and mitochondrial fractions from the rat adipocyte (1, 2). Addition of insulin to this subcellular system caused a plasma membrane-mediated decrease in the phosphorylation of a mitochondrial protein, identified as the a subunit of pyruvate dehydrogenase [pyruvate:lipoamide oxidoreductase (decarboxylating and acceptor-acetylating), EC 1.2.4.1]. This effect was consistent with the proposed model of insulin action on pyruvate dehydrogenase in the intact cell (3, 4). From these data, it was predicted that the activity of pyruvate dehydrogenase should be stimulated by the addition of insulin to the plasma membrane/mitochondria mixture. This study investigates the activity of pyruvate dehydrogenase in the plasma membrane/mitochondria mixture and the effect of insulin and other agents on this enzyme. EXPERIMENTAL PROCEDURESMaterials. Male Sprague-Dawley rats (120 g) were obtained from Eldridge Laboratory Animals (Barnhardt, MO). Collagenase, bovine serum alb...

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supporting

confidence: 77%

Activation of pyruvate dehydrogenase by direct addition of insulin to an isolated plasma membrane/mitochondria mixture: Evidence for generation of insulin's second messenger in a subcellular system

Seals

Jarett

1980

Proc. Natl. Acad. Sci. U.S.A.

147

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“…Is the decrease in pyruvate dehydrogenase activity and glucose oxidation to COz secondary to the high fat diet of suckling animals? Denton and Hughes (2) reported that rats placed on high fat diet for 6 d showed a rapid decrease in adipose tissue pyruvate dehydrogenase activity, which is primarily due to a decrease in the active form of the enzyme. Adipose tissue from rats on a high fat diet for 19-23 d had a significant decrease in total pyruvate dehydrogenase activity.…”

Section: Discussionmentioning

confidence: 99%

The Effect of Ketone Bodies and Fatty Acid on Intestinal Glucose Metabolism during Development

1984

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Summaryfrom glucose was markedly decreased and lactate production increased. In the present study we investigated developmeni.al Glucose oxidation by developing rat intestine changed dramat-change in glucose metabolism to C 0 2 , lactate, and pyruvate by ically during the period o f suckling and weaning. After weaning, intestine during the time of suckling and weaning, glucose oxidation to C 0 2 by intestinal slices increased over 3-fold. This was associated with an increase in lactate production from glucose and an increase in the rate o f pyruvate decarbox- MATERIALS AND METHODS ylation.Active pyruvate dehydrogenase in intestine o f developing rats also increases in activity at the time o f weaning, suggesting that the suppression o f glucose oxidation during the suckling period is controlled by pyruvate dehydrogenase. Glucose oxidation to Five millimolars glucose was found to give an optimal rate of glucose oxidation. In the small intestine, substrates are not only delivered by the The optimal concentration for pyruvate oxidation was 10 mbI. blood but are also immediately available from intraluminalThe metabolic flasks were sealed in the presence of room air absorption. Changes in the diet that occur during suckling and with rubber caps which were fitted with polypropylene center weaning have been shown to alter intracellular fatty acid levels wells (Kontes Glass Co.) (29). Because the rate of C 0 2 and lactate in intestinal mucosal cells. The suckling rat pup diet consists of production from glucose was constant for the incubation period, a high percentage of lipid (approximately 70% of total caloric it can be assumed that aerobic conditions were present. The content) (6). During suckling, the level of free fatty acids in flasks were removed from ice and the reaction was started by

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“…The effect of insulin on pyruvate dehydrogenase activity persists during the preparation and subsequent incubation of mitochondria from fat cells [63,64,178,179]. This phenomenon has allowed evidence to be obtained which strongly suggests that the effect of insulin does involve stimulation of the phosphatase (rather than inhibition of the kinase) [178].…”

Section: Changes In the Concentration Of Calcium Ions (Ca E + )mentioning

confidence: 96%

A partial view of the mechanism of insulin action

1981

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Insulin was discovered 60 years ago [1]; since then its structure has been determined by the pioneer work of Sanger [2] and by Hodgkin, Blundell and colleagues [3]. Moreover the principle effects of insulin on carbohydrate, fat and protein metabolism have been well recognised, at least ingeneral terms, for some 20 years [4][5][6][7], yet, we do not have a satisfactory description at the molecular level of how this hormone brings about its wide range of effects on target cells. This is certainly not due to any lack of attention to the problem by research workers. The literature on this subject is vast and, in the absence of any generally acceptable hypothesis, it also tends to be rather confused and certainly conflicting. Since it is quite unrealistic to survey the whole field, we make no apology for concentrating on certain aspects in this article.Insulin has both long and short term effects on the metabolism of its target cells. The long term effects involve changes in both general and specific protein synthesis and breakdown, while short term effects are those brought about solely through changes in the activity of pre-existing enzymes and membrane transporters. To a large extent, we will neglect all aspects of long term regulation including protein synthesis and amino acid metabolism. In fact, advances in these areas have been delayed by the lack of satisfactory preparations suitable for probing the mechanisms involved in the specific induction and repression of enzymes by insulin in vitro. This situation will probably change rapidly as a number of such preparations have been reported recently. Particularly promising are the 3T3-L1 preadipocyte cell line [8,9] and also the maintenance liver cell cultures from young rats in which glucokinase activity has been shown to be rapidly induced on exposure to insulin in the presence of glucose [10].In the rest of this review we will concentrate on those studies concerned with short term effects of insulin on carbohydrate and fat metabolism in the cells of liver, muscle and, particularly, adipose tissue. All these cells have specific insulin receptors on the outward face of the plasma membrane but we will not be considering the nature of these receptors nor their interaction with insulin nor the mechanisms which may govern the number of insulin receptors. These aspects have all been well covered in other recent reviews [11][12][13]. We shall address ourselves to the problem of the process or processes whereby alterations in the level of occupancy of the plasma membrane insulinreceptors lead to a wide range of intracellular changes. The assumption will be made that neither the whole insulin molecule nor part of it needsto enter the cells of its target tissue to bring about the effects of insulin. There seems little doubt that insulin bound to its receptor can be "internalized" into liver and probably other cells [14, 15], however, the process appears to be too slow to represent the means whereby insulin could bring about its short term effects. On the other hand, antibo...

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Pyruvate dehydrogenase and the hormonal regulation of fat synthesis in mammalian tissues

Cited by 78 publications

References 50 publications

Activation of pyruvate dehydrogenase by direct addition of insulin to an isolated plasma membrane/mitochondria mixture: Evidence for generation of insulin's second messenger in a subcellular system

Activation of pyruvate dehydrogenase by direct addition of insulin to an isolated plasma membrane/mitochondria mixture: Evidence for generation of insulin's second messenger in a subcellular system

The Effect of Ketone Bodies and Fatty Acid on Intestinal Glucose Metabolism during Development

A partial view of the mechanism of insulin action

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