Hydrogen in fatty acid synthesis

Pathway of Hydrogen in Fatty Acid Synthesis Consider a preparation that contains all the enzymes and cofactors necessary for fatty acid biosynthesis from added acetyl-CoA and malonyl-CoA. 

The ketoacyl-ACP is then reduced to yield a hydroxyl group. In turn, this is dehydrated to yield a carbon-carbon double bond, which is reduced to yield a saturated fatty acid chain. Thus, the sequence of chemical reactions is the reverse of that in P-oxidation (section 5.5.2). For both reduction reactions in fatty acid synthesis, NADPH is the hydrogen donor. One source of this NADPH is the pentose phosphate pathway (section 5.4.2) and the other is the oxidation of malate (arising from oxaloacetate) to pyruvate, catalysed by the malic enzyme (see Figure 5.27). 

A brief survey of pertinent aspects of comparative enzymology based on those references is presented here. The two enzyme systems which operate sequentially in fatty acid synthesis are acetyl-CoA carboxylase (ACC) and fatty acid synthetase (FAS). Straight-chain fatty acid synthesis operates using acetyl-CoA as the chain initiator, while branched-chain compounds are synthesized using isobutyryl-, isovaleryl- or 2-methylbutyryl-CoA esters. In either case malonyl-CaA acts as the unit for fatty acid chain extension and NADPH (reduced nicotinamide adenine dinucleotide phosphate) as the hydrogen donor. The repeated condensation of malonyl-CoA with the appropriate chain initiator by FAS ultimately produces the appropriate end-product, usually 16 0, palmitic acid, in the great majority of organisms (292, 293). 

This work describes the application to soil of compounds of a previous study (11) which dealt primarily with organic synthesis and physical properties of reaction products of pure fatty acids with BETA. In this study derivatives were prepared from various industrial fatty materials. In addition, water infiltration studies on sand, sandy soil, and clay soils were carried out on the previously prepared and new compounds. Finally, an investigation was initiated to determine the biological effects of one water-repelling chemical, the partially hydrogenated tallow-fatty acid-DETA reaction product, on seed germination and plant growth. 

Biosynthesis of coenzyme A (CoA) in mammalian cells incorporates pantothenic acid. Coenzyme A, an acyl group carrier, is a cofactor for various enzymatic reactions and serves as either a hydrogen donor or an acceptor. Pantothenic acid is also a stmctural component of acyl carrier protein (ACP). ACP is an essential component of the fatty acid synthetase complex, and is therefore required for fatty acid synthesis. Free pantothenic acid is isolated from hver, and is a pale yellow, viscous, and hygroscopic oil. 

The first step in de novo fatty acid synthesis is the production of malonyl-CoA from acetyl-CoA and bicarbonate. This committed step is catalyzed by acetyl-CoA carboxylase present in the cytoplasm of liver cells and adipocytes. After replacement of the CoA residue in acetyl-CoA by ACP (acyl carrier protein), malonyl-ACP is used to convert acetyl-ACP to butyryl-ACP by the fatty acid synthase complex. In this multistep reaction, NADPH is used as donor of hydrogen atoms and CO2 is produced. Butyryl-ACP is subsequently elongated to hexanoyl-ACP by a similar process in which malonyl-ACP serves as donor of two carbon atoms required for lengthening of the growing acyl chain. This process is repeated until palmitic acid... 

For the malonate group to be used for fatty acid synthesis, it must first be transferred from malonyl-CoA to malonyl-ACP by the 32.4-kDa monomeric malonyl-CoA ACP transacy-lase, the product of the fabD gene (Fig. 2). A stable malonyl-serine enzyme intermediate is formed during the course of the FabD reaction, and subsequent nucleophilic attack on this ester by the sulfhydryl of ACP yields malonyl-ACP. The high reactivity of the serine in malonyl-ACP transacylase is due to the active site being composed of a nucleophilic elbow as observed in alpha/beta hydrolases. The serine is hydrogen bonded to His-201 in a fashion similar to serine hydrolases. 

Bg, pyridoxine of NAD and its phosphorylate, NADP assists in hydrogen transfer of glycolysis, fatty acid synthesis, and tissue respiration Nitrogen metabolism transamination,... 

The synthesis of these surfactants involves several steps. The first step is the preparation of a substituted imidazoline, usually l-(hydroxyethyl)-2-alkyl imidazoline, starting from fatty acids or fatty acid methyl esters and aminoethylethanolamine (AEEA) (Figure 15.15). For the production of betaines, the choice of fatty material is in most cases hydrogenated coco fatty acid. The distribution composition of fatty acid chain lengths, given above in Table 15.2, is typical also for cocoam-phoacetates. 

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