J. Biol. Chem., Vol. 256, Issue 22, 11585-11590, 11, 1981
Inactivation of hepatic acetyl-CoA carboxylase by catecholamine and its agonists through the alpha-adrenergic receptors
S Ly and KH Kim
The effects of adrenergic agonists on acetyl-CoA carboxylase and fatty acid
synthesis were studied in isolated rat hepatocytes from mature rats (300 to
350 g). Norepinephrine and phenylephrine inactivate acetyl- CoA carboxylase
activity and inhibit fatty acid synthesis. The effects of both
norepinephrine and phenylephrine were blocked by the alpha- adrenergic
receptor blockers, phentolamine and phenoxybenzamine, and unaffected by the
beta-receptor blocker propranolol. This inactivation was not mimicked by
the beta-agonist isoproterenol. The measurable increase in cyclic AMP
levels caused by norepinephrine and phenylephrine was abolished by the
alpha-antagonist phentolamine and diminished by the beta-antagonist
propranolol. Calcium depletion potentiated the increase in cyclic AMP
levels by phenylephrine but abolished the phenylephrine inactivation of the
carboxylase. The inactivation of acetyl-CoA carboxylase by phenylephrine
was correlated with an increase in the incorporation of [32P]phosphate into
the enzyme. Thus, catecholamines and their agonists promote phosphorylation
and inactivation of acetyl-CoA carboxylase through the alpha-adrenergic
receptor, and the inactivation requires calcium.
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