Fatty acid Synthesis Mechanism:-2

Acetyl-CoA Carboxylase, which converts acetyl-CoA to malonyl-CoA, is the committed step of the fatty acid synthesis pathway. The acetyl-CoA and malonyl-CoA are transferred to Acyl carrier protein (ACP) by the action of acetyl-CoA transacylase and malonyl-CoA transacylase, respectively. The attachment of these carbon atoms to ACP allows them to enter the fatty acid synthesis cycle. The synthesis of fatty acids from acetyl-CoA and malonyl-CoA is carried out by fatty acid synthase (FAS). Note that this reaction is an energy requiring process (1 ATP per Malonyl-CoA formed).

This multifunctional enzyme catalyzes the seven different reactions whereby two carbon units from malonyl-CoA are linked together, ultimately to form palmitoyl-CoA. In some systems, the activities are present on separate enzyme units.The overall synthesis of palmitate from acetyl-CoA requires 14 NADPHs, and 7 ATPs.
Initiation Stage:- The elongation phase of fatty acid synthesis starts with the formation of acetyl ACP and malonyl ACP. Acetyl transacylase and malonyl transacylase catalyze these reactions.
Acetyl CoA + ACP U acetyl ACP + CoA
Malonyl CoA + ACP U malonyl ACP + CoA
? Step 1: loading of acetyl-CoA onto fatty acid synthase