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1. Isolated rat epididymal fat-cell mitochondria showed an inverse relationship between ATP content and pyruvate dehydrogenase activity consistent with competitive inhibition of pyruvate dehydrogenase kinase by ADP. At constant ATP concentration pyruvate rapidly activated pyruvate dehydrogenase in fat-cell mitochondria, an observation consistent with inhibition of fat-cell pyruvate dehydrogenase kinase by pyruvate. Pyruvate dehydrogenase in fat-cell mitochondria was also activated by nicotinate (100mum) and by extramitochondrial Na(+) (replacing K(+)) but not by ouabain or insulin. 2. In rat epididymal fat-pads incubated in vitro pyruvate dehydrogenase was activated by addition of insulin in the absence of substrate or in the presence of glucose (10mm) or fructose (10mm). Glucose and fructose activated the dehydrogenase in the absence or in the presence of insulin, and pyruvate also activated in the absence of insulin. It is concluded that extracellular glucose, fructose and pyruvate may activate the dehydrogenase by raising intracellular pyruvate and that insulin may activate the dehydrogenase by some other mechanism. 3. Ouabain (300mum) and medium in which K(+) was replaced by Na(+), activated pyruvate dehydrogenase in epididymal fat-pads. Prostaglandin E(1) (1mug/ml), 5-methylpyrazole-3-carboxylate (10mum) and nicotinate (10mum), which are as effective as insulin as inhibitors of lipolysis and which like insulin lower tissue concentration of cyclic AMP (adenosine 3':5'-cyclic monophosphate), did not activate pyruvate dehydrogenase. Higher concentrations of prostaglandin E(1) (10mug/ml) and nicotinate (100mum) produced some activation of the dehydrogenase. 4. It is concluded that the activation of pyruvate dehydrogenase by insulin is not due to the antilipolytic effect of the hormone and that the action of insulin in lowering adipose-cell concentrations of cyclic AMP does not afford an obvious explanation for the effect of the hormone on pyruvate dehydrogenase. The possibility that the effects of insulin, ouabain and K(+)-free medium may be mediated by Ca(2+) is discussed.
B R Martin, and
R M Denton, and
H T Pask, and
P J Randle
November 1973,
Canadian journal of biochemistry,
B R Martin, and
R M Denton, and
H T Pask, and
P J Randle
June 1971,
FEBS letters,
B R Martin, and
R M Denton, and
H T Pask, and
P J Randle
May 1987,
Hormone and metabolic research = Hormon- und Stoffwechselforschung = Hormones et metabolisme,
B R Martin, and
R M Denton, and
H T Pask, and
P J Randle
October 2017,
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B R Martin, and
R M Denton, and
H T Pask, and
P J Randle
May 1982,
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B R Martin, and
R M Denton, and
H T Pask, and
P J Randle
May 1975,
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B R Martin, and
R M Denton, and
H T Pask, and
P J Randle
May 1974,
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B R Martin, and
R M Denton, and
H T Pask, and
P J Randle
January 1973,
The Journal of biological chemistry,
B R Martin, and
R M Denton, and
H T Pask, and
P J Randle
August 1990,
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B R Martin, and
R M Denton, and
H T Pask, and
P J Randle
May 1979,
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