Free fatty acids biosynthesis

The regulation of triacylglycerol, phosphatidylcholine, and phosphatidylethanolamine biosynthesis is driven by the availability of free fatty acids. Those that escape oxidation are preferentiaUy converted to phos-phohpids, and when this requirement is satisfied they are used for triacylglycerol synthesis. 

Seven cycles are implicated in palmitic acid biosynthesis and, accordingly, seven malonyl residues and one acetyl are required. Acetyl is the end moiety in fatty acid biosynthesis. The palmitic acid thus synthetized is either transferred onto the outer CoA to produce acyl-CoA, or, more commonly, is hydrolyzed by the specific palmitate deacylase to yield a free fatty acid. 

Fatty acids are degraded by two-carbon units in a reverse manner analogous to their biosynthesis. The acyl-CoAs are first dehydrogenated to a,(3-unsaturated acyl-CoA, and then hydrated to (3-hydroxyacyl-CoA, followed by oxidation to (3-ketoacyl-CoA. The C-C bond between C-2 and C-3 of the latter compound is broken by a free CoA molecule via thiolysis to form an acyl-CoA that is two carbons shorter and acetyl-CoA. Unlike fatty acid biosynthesis, each step of the (3 oxidation of fatty acids is... 

The biosynthesis of fatty acids produced during alcoholic fermentation is initiated in the yeast cell by the formation of acetylcoenzyme A, which reacts with malonylcoenzyme A to form mainly saturated straight-chained fatty acids with an even number of four to 18 carbon atoms the appearance of relatively low levels of fatty acids with odd numbers of carbon atoms as well as unsaturated fatty acids depends on the fermentation conditions [6]. The volatile fatty acids contribute to the flavour of fermented beverages like wine or beer and their concentration usually lies between 100 and 250 mg 0.1 L p.e. In distilled spirits the concentration of free fatty acids is significantly lower owing to the esterification... 

The pathway The first committed step in fatty acid biosynthesis is the carboxylation of acetyl CoA to form malonyl CoA which is catalyzed by the biotin-containing enzyme acetyl CoA carboxylase. Acetyl CoA and malonyl CoA are then converted into their ACP derivatives. The elongation cycle in fatty acid synthesis involves four reactions condensation of acetyl-ACP and malonyl-ACP to form acetoacetyl-ACP releasing free ACP and C02, then reduction by NADPH to form D-3-hydroxybutyryl-ACP, followed by dehydration to crotonyl-ACP, and finally reduction by NADPH to form butyryl-ACP. Further rounds of elongation add more two-carbon units from malonyl-ACP on to the growing hydrocarbon chain, until the C16 palmitate is formed. Further elongation of fatty acids takes place on the cytosolic surface of the smooth endoplasmic reticulum (SER). 

Vitamin B12 is essential for the methylmalonyl-CoAmutase reaction. Methylmalonyl-CoA mutase is required during the degradation of odd-chain fatty acids and of branched-chain amino acids. Odd-chained fatty acids lead to propionyl-CoA as the last step of P-oxida-tion. Methylmalonyl-CoA can be derived from propionyl-CoA by a carboxylase reaction similar to that of fatty acid biosynthesis. The cofactor for this carboxylation reaction is biotin, just as for acetyl-CoA carboxylase. The reaction of methylmalonyl-CoA mutase uses a free radical intermediate to insert the methyl group into the dicar-boxylic acid chain. The product is succinyl-CoA, a Krebs cycle intermediate. The catabolisms of branched-chain lipids and of the branched-chain amino acids also require the methylmalonyl-CoA mutase, because these pathways also generate propionyl-CoA. 

Phospholipids — arachidonic acid - Arachidonic acid metabolites appear not to be stored within cells. Their biosynthesis depends upon the appearance of substrate at or near the microsomal synthetase complex(es). According to current thinking, arachidonic acid is stored in the phospholipid fraction of the cell from which the free fatty acid is liberated by the action of a phospholipase... 

Fatty acids in the body arise either from biosynthesis from acetyl-CoA or from breakdown of fats and phospholipids. Free fatty acids are rarely found in the body. Fatty acids are transported in the blood complexed to serum albumin. Fatty acids can be saturated (no double bonds) or unsaturated (contain double bonds). Unsaturated fatty acids of biological origin predominantly contain cis double bonds. Mammals are unable to synthesize some fatty acids, making these fatty acids essential components of their diet. 

The lignan (+)-sesamin and related lignans present in sesame seeds or its oil are specific inhibitors of A5-desaturase in polyunsaturated fatty acid biosynthesis in both microorganisms and animals [273,274], The results obtained in experiments with both a cell-free extract of the fungus Mortierella alpina and rat liver microsomes demonstrated that (+)-sesamin... 

MTD significantly decreased incorporation of [ C]acetate into triacylglycerol and free fatty acid compared with myristic acid [7], Decreased [ C]acetate incorporation was also noted with CLA, but to a lower extent compared with 13-MTD. Myristic acid enhanced transformation of free fatty acid into triacylglycerols more than did 13-MTD or CLA. 13-MTD decreased cholesterogenesis in breast cancer cells and decreased fatty acid biosynthesis. 

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