a subunit of acetyl-CoA carboxylase (ACC), a multifunctional enzyme system. Catalyzes the carboxylation of acetyl-CoA to malonyl-CoA, the rate-limiting step in fatty acid synthesis. Activity is increased by oligomerization. Activated by citrate. Citrate and MID1IP1 promote oligomerization. Inhibited by malonyl-CoA. ACC1 is the predominant form expressed in liver, adipocyte and mammary gland. Phosphorylation by AMPK or PKA inhibits the enzymatic activity of ACC. ACC2 is the major isoform in skeletal muscle and heart. Phosphorylation regulates its activity. Two isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.