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. Phosphorylation by AMPK or PKA inhibits the enzymatic activity of ACC. ACC-alpha is the predominant isoform in liver, adipocyte and mammary gland. ACC-beta is the major isoform in skeletal muscle and heart. Phosphorylation regulates its activity. Note: This description may include information from UniProtKB.