Coenzyme A Activation of Acetyl-CoA Carboxylase

Acetyl-CoA carboxylase is activated by physiological concentrations of CoA. Activation of partially purified enzyme by CoA is accompanied by a decrease in the Km for acetyl-CoA from 0.2 mM to about 4 microM, which is the physiological concentration of acetyl-CoA in the cytosol. CoA activation of the purified enzyme is accompanied by an increase in the Vmax, without changing the Km for acetyl-CoA. The Km for acetyl-CoA of the purified enzyme is about 10 to 40 microM. The purification procedure results in a decrease in the Km for acetyl-CoA; under these conditions, CoA activation does not cause further lowering of the Km. CoA activation is accompanied by polymerization of the enzyme. However, CoA activation is not causally related to polymerization. There is one CoA binding site/subunit of acetyl-CoA carboxylase. CoA binding at that site is not affected by the presence of citrate, but palmityl-CoA inhibits CoA binding. CoA alone cannot reverse palmityl-CoA inhibition of the carboxylase. Bovine serum albumin and CoA together can activate the palmityl-CoA-inhibited enzyme. This indicates that the involvement of bovine serum albumin-like protein, CoA, and palmityl-CoA may play a physiologically significant role in the control of acetyl-CoA carboxylase.