Adrenaline and the regulation of acetyl-coenzyme A carboxylase in rat epididymal adipose tissue. Inactivation of the enzyme is associated with phosphorylation and can be reversed on dephosphorylation

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Abstract
Exposure of rat epididymal fat-pads or isolated fat-cells to adrenaline [epinephrine] causes a decrease in acetyl-CoA carboxylase activity measured both in initial extracts and in extracts incubated with potassium citrate; the concentration of citrate required to give half-maximal activation may also be increased. Incorporation of 32Pi into acetyl-CoA carboxylase within intact fat-cells was studied and apparently adrenaline increases the extent of phosphorylation of the enzyme. Dephosphorylation of 32P-labeled acetyl-CoA carboxylase was studied in cell extracts. The rate of release of 32P is increased by 5 mM-MgCl2 and further enhanced by 5 mM-MgCl2 plus 10-100 .mu.M-Ca2+, but it is inhibited by the presence of bivalent metal ion chelators, e.g., EDTA and citrate. The effects of adrenaline on the kinetic properties of acetyl-CoA carboxylase disappear if pad or cell extracts are treated with Mg2+ and Ca2+ under conditions that lead to dephosphorylation of the enzyme. Apparently adrenaline inactivates acetyl-CoA carboxylase in adipose-tissue preparations by increasing the degree of phosphorylation of the enzyme.

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