Acetyl-CoA carboxylase (ACC) is a complex multifunctional enzyme system which catalyzes the carboxylation of acetyl-CoA to malonyl-CoA, the rate-limiting step in fatty acid synthesis. Exercise diminishes the activity of acetyl-CoA carboxylase in human muscle. ACC alpha (ACC1) is the rate-limiting enzyme in the biogenesis of long-chain fatty acids, and ACC beta (ACC2) is thought to control mitochondrial fatty acid oxidation. These two isoforms of ACC control the amount of fatty acids in the cells. ACC beta is thought to control fatty acid oxidation by means of the ability of malonyl-CoA to inhibit carnitine-palmitoyl-CoA transferase I, the rate-limiting step in fatty acid uptake and oxidation by mitochondria. The gene encoding ACC beta maps to human chromosome 12 and encodes a mitochondiral protein expressed in heart and skeletal muscle. The catalytic core of ACC beta is homologous to that of ACC alpha, except for an additional peptide of about 150 amino acids at the N-terminusSynonyms: ACACB, ACC2, ACCB