Figure 1. The initiation module of type II fatty acid synthesis.
The priming reaction for the elongation cycle is performed by the by the initiating condensing enzyme, FabH, which condenses an acyl-CoA with malonyl-ACP. In bacteria that produce straight chain fatty acids (SCFA), acetyl-CoA is employed. Bacteria producing branched-chain fatty acids (BCFA) utilize an amino acid derived branched chain acyl-CoA precursor. Malonyl-CoA is formed by acetyl-CoA carboxylase, which is composed of four different protein subunits encoded by separate genes (AccABCD). Malonyl-ACP is formed by the transacylase, FadD.