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The biosynthesis of FFA

90% of AcetylCoA is used for Citric acid cycle (CAC) which yields 3NADH2, FPH2, ATP and 2CO2. 10% of AcetylCoA is used for synthesis of FFA, ketone bodies and Cholesterol.

The biosynthesis of FFA is mainly located in cytosol of cells. This process occurs intensively in liver, adipose tissue, brain, lungs and mammary glands. Initial material for FFA synthesis is AcetylCoA.

The biosynthesis of FFA includes 3 stages:

1 – providing the initial material. The initial material is acetylCoA. It is formed in mitochondrions, then it removes to cytosol. This removal occurs due to formation of citric acid in mitochondrions (acetylCoA +oxaloacetic acidàcitric acid). Citric acid halves to acetylCoA and oxaloacetic acid again in cytosol. Oxaloacetic acid can be returned in mitochondrions through the formation of malate or used as a source for formation of glucose, glycerol and amino acids;

2 – formation of substrate for biosynthesis of FFA. The substrate is malonylCoA. It is formed due to the interaction of acetylCoA with CO2. This reaction requires ATP;

3 - condensation of AcetylCoA with MalonylCoA and consecutive lengthening of the chain of FFA. This stage includes the following reactions: a) condensation of acetylCoA with malonylCoA due to the binding with acyl-carrier protein (ACP). It results in formation of acetoacetylACP. B) acetoacetylACP is reduced by NADPH2, yielding beta-hydroxybutyrylACP; C) beta-hydroxybutyrylACP undergoes dehydration (removal of water), yielding dehydrobutyrylACP; d) dehydrobutyrylACP is reduced by NADPH2 to butyrylACP. Then, the other malonylCoA binds to free SH-group of ACP and reactions are repeated by the same way (decarboxylation of malonylCoA and condensation of residue of malonylCoA with butyryl, reduction, dehydration, reduction). Thus, during one cycle of biosynthesis of FFA the chain of fatty acid is enlarged on 2 carbon atoms and 1 ATP and 2 NADPH2 used. We can account the quantity of ATP and NADPH2 used for synthesis of FFA. For example, for the synthesis of palmitic acid (C16) we need 7 ATP and 14 NADPH2 (7 cycles of synthesis). Each cycle demands 1 ATP for formation of malonylCoA and uses 2 NADPH2. Altogether will be 7 ATP and 14 NADPH2

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