THE ROLE OF CYCLIC-AMP IN RAT LIVER ACETYL-COENZYME-A CARBOXYLASE REGULATION
Evidence exists that fasting, glucagon, and cyclic-3',5'-adenosine monophosphate (cAMP) inhibit lipogenesis and acetyl-CoA carboxylase activity in vivo and in vitro. Because the mechanism of action of glucagon is hormone-cAMP-mediated protein phosphorylation, covalent modification may be r...
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| Format: | Dissertation |
| Language: | English |
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ProQuest Dissertations & Theses
01-01-1981
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| Online Access: | Get full text |
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| Summary: | Evidence exists that fasting, glucagon, and cyclic-3',5'-adenosine monophosphate (cAMP) inhibit lipogenesis and acetyl-CoA carboxylase activity in vivo and in vitro. Because the mechanism of action of glucagon is hormone-cAMP-mediated protein phosphorylation, covalent modification may be responsible for short-term regulation of carboxylase. Available data indicate, however, that cAMP-independent protein kinase phosphorylates acetyl-CoA carboxylase. The purpose of this project was to determine the regulatory role of cAMP on rat liver acetyl-CoA carboxylase activity and phosphorylation in near homogeneous and partially purified preparations. Partially purified enzyme was either dialyzed or chromatographed on Sephadex G-25 prior to assaying. Cyclic AMP-independent and -dependent protein kinases co-purified with near homogeneous acetyl-CoA carboxylase. Protein phosphorylation and inactivation of carboxylase were catalyzed by cAMP-independent protein kinase. Cyclic AMP-dependent protein kinase did not affect activity but greatly stimulated protein phosphorylation of the enzyme. Endogenous activated catalytic subunit of cAMP-dependent protein kinase did not affect phosphorylation-inactivation. Data with partially purified systems indicated that cAMP significantly inhibited activity of acetyl-CoA carboxylase from ad libitum fed animals, but did not stimulate radioactive phosphate incorporation. With fasted-refed rats, the inhibition of enzymatic activity by cAMP was partially or totally abolished, while protein phosphorylation was not significantly affected. Subjecting rats to a 48 hour fast-48 hour refeed period prior to sacrifice stimulated the production of a form of acetyl-CoA carboxylase not responsive to cAMP inhibition. Thus, cAMP stimulated phosphorylation of near homogeneous acetyl-CoA carboxylase but not partially purified enzyme. Cyclic-AMP inhibited activity of partially purified acetyl-CoA carboxylase from ad libitum fed rat but not that of near homogeneous enzyme. The activity of partially purified enzyme from fasted-refed rats was unresponsive to inhibition by ATP-magnesium with or without cAMP. Pre-incubating partially purified acetyl-CoA carboxylase altered the specificity of antigen for antibody such that less antigen was precipitated by antibody. Presumably, the effect was due to a change in the structural configuration of antigenic molecules. |
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| ISBN: | 9798661815941 |