Activator of acetyl CoA carboxylase is

Acetyl CoA Carboxylase It is the key enzyme; citrate activates this enzyme. The citrate level is high only when both acetyl CoA and ATP are abundant. Covalent modification is another regulatory mechanism. Phosphorylation inactivates acetyl CoA carboxylase (similar to glycogen synthase under the effect of glucagon). Hence fatty acid synthesis decreases when glucose level is low. The enzyme is inhibited by palmitoyl CoA, the end product.Ref: DM Vasudevan - Textbook of Biochemistry, 8th edition, page no: 139