Fatty Acid Synthesis (Reductant sources) 

The synthesis of one palmitate requires 14 NADPH, a reductant (reducing agent). The pentose phosphate pathway  is a major supplier of the NADPH.

Two NADPH are produced for each molecule of glucose 6- phosphate that enters this pathway. The cytosolic conversion of malate to pyruvate, in which malate is oxidized and decarboxylated by cytosolic malic enzyme (NADP+-dependent malate dehydrogenase), also produces cytosolic NADPH (and CO2), as shown in Figure 1. [Note: Malate can arise from the reduction of OAA by cytosolic NADH-dependent malate dehydrogenase (see Fig. 16.10). One source of the cytosolic NADH required for this reaction is glycolysis (see p. 101). OAA, in turn, can arise from citrate cleavage by ATP citrate lyase.] A summary of the interrelationship between glucose metabolism and palmitate synthesis is shown in Figure 2.

Figure 1: Cytosolic conversion of oxaloacetate to pyruvate with the generation of nicotinamide adenine dinucleotide phosphate (NADPH). [Note: The pentose phosphate pathway is also a source of NADPH.] NAD(H) = nicotinamide adenine dinucleotide; CO2 = carbon dioxide.

Figure 2: Interrelationship between glucose metabolism and palmitate synthesis. CoA = coenzyme A; NAD(H) = nicotinamide adenine nucleotide; NADP(H) = nicotinamide adenine dinucleotide phosphate; ADP = adenosine diphosphate; Pi = inorganic phosphate; CO2 = carbon dioxide; TCA = tricarboxylic acid; PC = pyruvate carboxylase; PDH = pyruvate dehydrogenase.