Effects of Magnesium Ions, Adenosine Triphosphate, Palmitoylcarnitine, and Palmitoyl Coenzyme A on Acetyl Coenzyme A Carboxylase

Acetyl coenzyme A carboxylase is activated strongly by incubation with magnesium ions in the absence of citrate and by incubation with citrate in the absence of magnesium ions. The activation by magnesium ions is concentration- and time-dependent. Under optimum conditions the effects of citrate and magnesium ions are not additive. Although the activation by magnesium ions occurs in the absence of citrate, the enzyme requires citrate for the complete reaction. Addition of adenosine triphosphate to the activation medium containing either magnesium ions or citrate or both strongly inhibits the activation of acetyl coenzyme A carboxylase. The inhibition is not due to removal of magnesium ions by chelation with adenosine triphosphate. Enzyme which has been activated with magnesium ions sediments at about the same rate as the inactive enzyme. Palmitoyl carnitine and cetyl trimethylammonium ions also stimulate the activity of the enzyme. This type of activation occurs rapidly, unlike the activation of the rat liver enzyme by magnesium ions and citrate. The maximum degree of stimulation by palmitoyl carnitine is observed when acetyl coenzyme A carboxylase has not been fully activated with other activators, but a 2- to 3-fold stimulation is observed even with enzyme which has been activated optimally with magnesium ions and citrate.