Fig 1.

The acetyl-CoA carboxylase (ACC) reaction. The synthesis of malonyl-CoA is carried out in two distinct partial reactions. The acetyl-CoA carboxylase (ACC) reaction is initiated by the carboxylation of biotin bound to the accB-encoded biotin carboxylase carrier protein (BCCP) by the accC-encoded biotin carboxylase (BC) (A). In the second partial reaction, the carbonyl group is transferred from the biotin moiety of the carrier protein to acetyl-CoA by the carboxyltransferase (CT) component (encoded by accA and accD), to give malonyl-CoA (B).