Acetyl coenzyme fatty acid origin

The leaving group is the enolate anion of acetyl-CoA, and the reaction thus cleaves off a two-carbon fragment from the original fatty acyl-CoA. Since the nucleophile is coenzyme A, the other product is also a coenzyme A ester. In fact, the reaction generates a new fatty acyl-CoA, shorter by two carbons, which can re-enter the P-oxidation cycle. Most natural fatty acids have an even number of carbons, so the process continues until the original fatty acid chain is cleaved completely to acetyl-CoA fragments. 

The fourth and last step of the /3-oxidation cycle is catalyzed by acyl-CoA acetyltransferase, more commonly called thiolase, which promotes reaction of /3-ketoacyl-CoA with a molecule of free coenzyme A to split off the carboxyl-terminal two-carbon fragment of the original fatty acid as acetyl-CoA The other product is the coenzyme A thioester of the fatty acid, now shortened by two carbon atoms (Fig. 17-8a). This reaction is called thiolysis, by analogy with the process of hydrolysis, because the /3-ketoacyl-CoA is cleaved by reaction with the thiol group of coenzyme A... 

The TCA cycle. In each turn of the cycle, acetyl-CoA from the glycolytic pathway or from /3 oxidation of fatty acids enters and two fully oxidized carbon atoms leave (as C02). ATP is generated at one point in the cycle, and coenzyme molecules are reduced. The two C02 molecules lost in each cycle originate from the oxaloacetate of the previous cycle rather than from incoming acetyl from acetyl-CoA. This point is emphasized by the use of color. 

A deficiency in pantothenic acid causes the yeast to accumulate acetic acid but it has not been proven that the (unauthorized) addition of pantothenic acid to a fermenting must lowers the wine s volatile acidity originating from yeast. The production by yeasts of abnormally high levels of volatile acidity is probably due to the must s deficiencies in certain lipids. These deficiencies are most likely linked to deficiencies in pantothenic acid, which is involved in the formation of acetyl coenzyme A, responsible for fatty acid and lipid synthesis. 

The cycle was originally proposed as a mechanism for the terminal oxidation of carbohydrate. It was always obvious that it must also apply to parts of the protein molecule because several amino acids yield members of the cycle directly—glutamic acid, aspartic acid, and alanine—or indirectly—histidine, proline, arginine, and others. Work carried out during the last decade with the help of specially prepared tissue extracts and of isotopes has produced conclusive evidence in support of the conception that the tricarboxylic acid cycle is also the terminal mechanism of the oxidation of fatty acids and ketone bodies. These substances all form the same derivative of acetic acid—acetyl coenzyme A— which can condense with oxalacetate to form citrate. The pathway leading from various... 

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