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Mechanism for Acute Control of Fatty Acid Synthesis by Glucagon and 3:5-Cyclic AMP in the Liver Cell

Paul A. Watkins, David M. Tarlow and M. Daniel Lane
Proceedings of the National Academy of Sciences of the United States of America
Vol. 74, No. 4 (Apr., 1977), pp. 1497-1501
Stable URL: http://www.jstor.org/stable/66730
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Mechanism for Acute Control of Fatty Acid Synthesis by Glucagon and 3′:5′-Cyclic AMP in the Liver Cell
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Abstract

Labeling experiments with chicken liver cell monolayers and suspensions show that glucagon and N6,O2-dibutyryladenosine 3′:5′-cyclic monophosphate (dibutyryl cyclic AMP) block fatty acid synthesis from acetate without appreciably affecting cholesterogenesis from acetate or acylglyceride synthesis from palmitate. Neither acetyl-CoA carboxylase [acetyl-CoA:carbon-dioxide ligase (ADP-forming), EC 6.4.1.2] activity assayed in the presence of citrate nor fatty acid synthetase activity is decreased in extracts of cells treated with glucagon. However, the cytoplasmic concentration of citrate, a required allosteric activator of acetyl-CoA carboxylase, is depressed more than 90% by glucagon or dibutyryl cyclic AMP. Pyruvate or lactate largely prevents the inhibitory action of these effectors on fatty acid synthesis by causing a large increase in cytoplasmic citrate level. Thus, it appears that glucagon, acting via cyclic AMP, inhibits fatty acid synthesis by blocking the formation of citrate, an essential activator of acetyl-CoA carboxylase.

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