Palmitate synthesis

Figure 6.10 (a) FAS reaction outline (b) Palmitate synthesis by FAS complex the individual reactions of the FAS complex are ... 

FIGURE 21-3 The overall process of palmitate synthesis. The fatty acyl chain grows by two-carbon units donated by activated malonate, with loss of C02 at each step. The initial acetyl group is shaded yellow, C-l and C-2 of malonate are shaded pink, and the carbon released as C02 is shaded green. After each two-carbon addition, reductions convert the growing chain to a saturated fatty acid of four, then six, then eight carbons, and so on. The final product is palmitate (16 0). 

Interrelationship between glucose metabolism and palmitate synthesis. 

PGase activity assay, 335-348 values for acetylation and methylation in some foods, 743 (table) Pectinesterase (PE), characterized, 342 PEG-palmitate, synthesis of, 308 Peptidases, see also Proteinases activity assays... 

Except for malonyl-CoA formation, all the individual reactions for palmitate synthesis reside on a single multifunctional protein (fatty acid synthase) in animal cells. It has been shown that a dimer of the multifunctional protein is required to catalyze palmitate synthesis. Explain the molecular basis of this observation. 

The typical secondary metabolites of soft corals are diterpenoids, although some species also produce sesquiterpenoids. The sesquiterpene portion of furoquinol (Structure 2.102) is labeled by [2-3H]mevalonolactone in Sinularia capillosa,m while Heteroxenia sp. converts acetate and meva-lonate into cubebol (Structure 2.103) and clavukerin A (Structure 2.104).188 In contrast, acetate is used for cetyl palmitate synthesis in Alcyonium molle, but not for de novo diterpene biosynthesis.188... 

The overall reaction for palmitate synthesis from acetyl-CoA is... 

The remaining reactions in fatty acid synthesis take place on the fatty acid synthase multienzyme complex. This complex, the site of seven enzyme activities and ACP, is a 500-kD dimer. Because the enormous polypeptides in the dimer are arranged in a head-to-tail configuration, two fatty acids can be constructed simultaneously. A proposed mechanism for palmitate synthesis is shown in Figure 12.13. 

Acetyl CoA is the precursor of fatty acids. For palmitate synthesis (C16), seven acetyl CoAs are converted to malonyl CoA by acetyl CoA carboxylase. These seven malonyl CoAs, plus one acetyl CoA, are combined stepwise on FAS, with addition of one malonyl CoA at a time. 

See also Acetyl-CoA, Fats, Albumin, Fatty Acid Activation, Oxidation of Saturated Fatty Acids, Oxidation of Unsaturated Fatty Acids, Fatty Acid Biosynthesis Strategy, Palmitate Synthesis from Acetyl-CoA, Fatty Acid Desaturation, Essential Fatty Acids, Control of Fatty Acid Synthesis, Molecular Structures and Properties of Lipids (from Chapter 10)... 

See also Fatty Acids, Table 10.1, Synthesis of Long Chain Fatty Acids, Fatty Acid Desaturation, Fatty Acid Synthase, Palmitate Synthesis from Acetyl-CoA... 

Elongation of the acyl group to make fatty acids longer than 16 carbons (palmitate) occurs apart from palmitate synthesis. Whereas palmitate synthesis occurs in the cytosol, elongation occurs in both the mitochondria and endoplasmic reticulum (ER). The ER is the dominant system. Elongation in the ER differs from cytosolic synthesis in employing coenzyme A (instead of acyl carrier protein) and separate enzymes (instead of a complex). The condensation reaction occurs between malonyl-CoA and an acyl-CoA to form a / -ketoacyl-CoA (see here and here). Two enzymes catalyze this step in the endoplasmic reticulum, one of which is specific for unsaturated fatty acyl-CoAs. 

See also Fatty Acid Biosynthesis Strategy, Palmitate Synthesis from Acetyl-CoA... 

FIGURE 21.15 The pathway of palmitate synthesis from acetyl-CoA and malonyl-CoA. 

Wakil s pioneering studies on fatty acid synthesis included the crucial observation that bicarbonate is required for the synthesis of palmitoyl CoA. He was surprised to find that very low levels of bicarbonate could sustain palmitate synthesis that is, there was no correlation between the amount of bicarbonate required and the amount of palmitate produced. Later he also found that " C-labeled bicarbonate is not incorporated into palmitate. Explain these observations. 

Fig. 1 Path of bacterial cetyl palmitate synthesis from -hexadecane (Stewart et al 1959).

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