Comparative Studies of Catalytic Properties of Guinea Pig Liver Intra- and Extramitochondrial Phosphoenolpyruvate Carboxykinases<sup>*</sup>

Holten, Darold; Nordlie, Robert C.

doi:10.1021/bi00880a018

Cited by 108 publications

(34 citation statements)

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“…Although malate inhibits all four enzymes to about the same extent at low oxaloacetate concentrations, the inhibition is not evident at high oxaloacetate concentrations with the mitochondrial enzymes, and when Mn2+ is used as cation for the cytosol enzymes (Table 3 (Holten & Nordlie, 1965;. One possible explanation is that phosphoenolpyruvate carboxykinase could exhibit co-operative behaviour with respect to oxaloacetate and give non-linear doublereciprocal plots.…”

Section: Resultsmentioning

confidence: 99%

“…In an attempt to resolve different metabolic functions of cytosol and mitochondrial phosphoenolpyruvate carboxykinases, Holten & Nordlie (1965) undertook a comparative study between the two enzymes from guinea-pig liver. Although most kinetic properties were similar, they found that only the mitochondrial enzyme was inhibited by 1.33mM-AMP and that the mitochondrial enzyme was more active with Mg2+ than with Mn2+ at pH 8.…”

Section: Resultsmentioning

confidence: 99%

“…Michaelis constants for oxaloacetate have been reported for phosphoenolpyruvate carboxykinase isolated from the livers of several mammals. Values in the range 9 x 10-4M to 4 x 10-3 M were obtained for the enzymes purified from guinea-pig liver mitochondria or cytosol (Holten & Nordlie, 1965) and chicken liver mitochondria (Felicioli, Barsacchi & Ipata, 1970), and values of approx. 1.4 x 10-4M were reported for the enzymes from pig liver mitochondria (Chang, Maruyama, Miller & Lane, 1966) or the cytosol fraction ofrat liver (Foster, Lardy, Ray & Johnston, 1967).…”

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Kinetic studies with cytosol and mitochondrial phosphoenolpyruvate carboxykinases

Ballard

1970

Biochemical Journal

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Kinetic studies with cytosol and mitochondrial phosphoenolpyruvate carboxykinases

Ballard

1970

Biochemical Journal

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“…Other pointcrs in this direction are the kinetic differences between the mitochondrial and the cytoplasmic phosphoenolpyruvate carboxykinase of the guinea pig liver [33] and the marked decrease of pyruvate kinase activity in rat liver during active gluconeogenesis [34]. None of these mechanisms can be operating in the chick enibryo liver since no extramitochondrial phosphoenolpyruvate carboxykinase is present in this tissue and since the pathway pyruvate + oxaloacetate + phosphoenolpyruvate takes place in the mitochondria while it is well known that the pyruvate kinase is located in the cytoplasm.…”

Section: Discussionmentioning

confidence: 99%

The Synthesis of Phosphoenolpyruvate in the Gluconeogenesis

Felicioli¹,

Gabrielli²,

Rossi³

1967

European Journal of Biochemistry

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Livers of chick embryos a t different stages of incubation have been fractionated into mitochondrial and "soluble" fractions by centrifugation.The pyruvate carboxylase and phosphoenolpyruvate carboxykinase activities, which constitute the major pathway for the synthesis of phosphoenolpyruvate, have been measured in both preparations.The pyruvate carboxylase activity occurs only in the mitochondria and parallels the gluconeogenetic ability.The bulk of phosphoenolpyruvate carboxykinase activity appears in the mitochondria. Only traces can be detected in the "soluble" fraction. The level of the mitochondrial phosphoenolpyruvate carboxykinase activity varies during the incubation period in accordance with its presumed role as a major source of phosphoenolpyruvate in the gluconeogenesis.The hypothesis that the pathway of synthesis of phosphoenolpyruvate in the process of gluconeogenesis is mainly located in the mitochondria of chick embryo liver is proposed.The sequence of reactions leading to phosphoenolpyruvate synthesis from pyruvate is one of the most intensively studied steps in the overall process of gluconeogenesis and the following sequence of reactions is now generally accepted :. Phosphoenolpyruvate + GDP + CO,.

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“…The steady-state concentration of cytosolic oxaloacetate (Table 5) is well below the K, of phosphoenolpyruvate carboxykinase for this intermediary [36], which is the reason why variations in its concentration should be very important for the control of flux at this step. On these grounds the observed effect of glucagon decreasing oxaloacetate concentration does not seem to agree with the postulate that the hormone activates this enzymic step [6,39].…”

Section: Sites Of Glucagon Actionmentioning

confidence: 99%

Glucagon and Insulin Control of Gluconeogenesis in the Perfused Isolated Rat Liver. Effects on Cellular Metabolite Distribution

1975

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The metabolic effects of glucagon and glucagon plus insulin on the isolated rat livers perfused with 10 mM sodium L-lactate as substrate were studied. Glucagon stimulated gluconeogenesis, ketogenesis and ureogenesis at the concentration used of 2.1 nM. The addition of insulin to give a glucagon-to-insulin ratio of 0.2 reversed all the glucagon effects.The glucagon enhancement of gluconeogenesis was accompanied by a rise in the cytosolic and mitochondrial state of reduction of the NAD system and a fall in the [ATP]/[ADP] ratio. The analysis of the intermediary metabolite concentrations suggested, as possible sites of glucagon action, the steps between pyruvate and phosphoenolpyruvate as well as the reactions catalyzed by phosphofructokinase and/or fructose bisphosphatase. All the changes in metabolite contents were abolished when insulin was present.Glucagon increased the intramitochondrial concentration of all the metabolites, whose intracellular distribution was calculated. The finding of a significant rise in the calculated intramitochondrial concentration of oxaloacetate points to pyruvate carboxylation as an important site of glucagon interaction with the gluconeogenic pathway. A primary event in the glucagon action redistributing intracellular metabolites seems to be the mitochondrial entry of malate. The possibility is discussed that the changes in metabolite cellular distribution were brought about by the increased cellular state of reduction caused by the hormone.Since an early study, in which the role of glucagon on hepatic gluconeogenesis was postulated [l -41, a considerable amount of information has been accumulated regarding its mechanism of action. However, the efforts do not seem to have been succesful, since as yet no satisfactory explanation has been found to elucidate the mechanism leading to the enhancement of the hepatic gluconeogenic flux under the different situations in which the hormone is known to be active.Recent work has pointed to the activation of some metabolic event between pyruvate and phosphoenolpyruvate as the cause for the observed effect of glucagon stimulation of the gluconeogenic flux from subEnzymes. Aconitate hydratase (EC 4.2

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Comparative Studies of Catalytic Properties of Guinea Pig Liver Intra- and Extramitochondrial Phosphoenolpyruvate Carboxykinases^*

Cited by 108 publications

References 18 publications

Kinetic studies with cytosol and mitochondrial phosphoenolpyruvate carboxykinases

Kinetic studies with cytosol and mitochondrial phosphoenolpyruvate carboxykinases

The Synthesis of Phosphoenolpyruvate in the Gluconeogenesis

Glucagon and Insulin Control of Gluconeogenesis in the Perfused Isolated Rat Liver. Effects on Cellular Metabolite Distribution

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Comparative Studies of Catalytic Properties of Guinea Pig Liver Intra- and Extramitochondrial Phosphoenolpyruvate Carboxykinases*

Cited by 108 publications

References 18 publications

Kinetic studies with cytosol and mitochondrial phosphoenolpyruvate carboxykinases

Kinetic studies with cytosol and mitochondrial phosphoenolpyruvate carboxykinases

The Synthesis of Phosphoenolpyruvate in the Gluconeogenesis

Glucagon and Insulin Control of Gluconeogenesis in the Perfused Isolated Rat Liver. Effects on Cellular Metabolite Distribution

Contact Info

Product

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Comparative Studies of Catalytic Properties of Guinea Pig Liver Intra- and Extramitochondrial Phosphoenolpyruvate Carboxykinases^*