Acetyl coenzyme preparation

ATP and magnesium were required for the activation of acetate. Acetylations were inhibited by mercuric chloride suggesting an SH group was involved in the reaction either on the enzyme or, like lipoic acid, as a cofactor. Experiments from Lipmann s laboratory then demonstrated that a relatively heat-stable coenzyme was needed—a coenzyme for acetylation—coenzyme A (1945). The thiol-dependence appeared to be associated with the coenzyme. There was also a strong correlation between active coenzyme preparations and the presence in them of pantothenic acid—a widely distributed molecule which was a growth factor for some microorganisms and which, by 1942-1943, had been shown to be required for the oxidation of pyruvate. 

Butyric acid is one of the simplest fatty acids. Fatty acids, which are the building units of fats and oils, are natural compounds of carbon chains with a carboxyl group (-COOH) at one end. Most natural fatty acids have an unbranched carbon chain and contain an even number of carbon atoms because during biosynthesis they are built in two carbon units from acetyl coenzyme A (CoA). Butyric acid is an unsaturated fatty acid, which means all carbon-carbon bonds are single bonds. Common names for fatty acids stem from their natural sources. In addition to butyric acid, some other common saturated fatty acids include lauric acid, palmitic acid, and stearic acid. Lauric acid was first discovered in Lauraceae (Laurus nobilis) seeds, palmitic oil was prepared from palm oil, and stearic acid was discovered in animal fat and gets its name from the Greek word stear for tallow. 

In the early 1940s, before the discovery of 14C and when acetyl-coenzyme A was unknown, two research groups used the stable isotope 13C and mass spectrometers to study carbon flow in the TCA cycle. Pyruvate and 13C02 were added to pigeon liver preparations to form carboxy-labeled oxaloacetate. Malonate was added to stop the TCA cycle at succinate. The expected result was that half of the 13C would be found in succinate and the other half in C02 (fig. 13.10). 

Chloramphenicol, an antibiotic originally produced from a streptomyces, is now prepared synthetically. It is a broad spectrum antibiotic, including activity against Ps. aeruginosa. That cell free extracts of E. coli strains inactive chloramphenicol in the presence of acetyl Coenzyme A has been well documented [223]. 

D-Glucosamine 6-phosphate can be readily acetylated by a AT-acetylase obtained from a preparation of yeast hexokinase. The resulting iV-acetyl-D-glucosamine 6-phosphate is identified by its Morgan-Elson reaction. The acetyl-coenzyme A which appears to be required for this reaction may be generated by acetate, adenosine-5-triphosphoric acid, and coenzyme A (in the presence of an acetate-activating enzyme). 

The two thiolate-bridged nickel-copper complexes in Fig. 6.6 have been prepared by reaction of [N2S2]Ni-type complexes with [Cu(CO)(PhTtBu)], the latter available via the carbonylation of [Cu(MeCN)(PhTt Bu)]. These complexes can be employed as model for the catalytic site of the acetyl coenzyme A synthase.14... 

Snoswell, A. Tubbs, P.K. (1978) Biochem. J. 171, 299-303. Deacylation of acetyl-coenzyme A and acetylcamitine by liver preparations. 

In 1951, Feodor Lynen (1911-1979) and his coworker E. Reichert demon-started that S-acetyl coenzyme A is a more generally implicated form of active acetate than acetyl phosphate that was recognized in this role by Fritz Lipmann in 1940. The thiol ester character of 5-acetyl Co A called the attention of Th. Wieland to energy-rich S-acyl compounds as promising intermediates for the formation of the peptide bond. In 1951, the same year when the isolation of 5-acetyl CoA was published [3], Wieland and his coworkers described [4] the preparation of thiophenyl esters of benzyloxycarbonyl-amino acids and benzyloxycarbonyl-peptides and their application in the synthesis of blocked peptides ... 

Indeed both -lactylthiamine pyrophosphate (XX) and a-hydroxyethyl-thiamine pyrophosphate (XXI) have been isolated and identified as products after incubation of pyruvate with a purified carboxylase preparation " . When [2- - C]pyruvate is used, the radioactivity is found in the thiazole part of the molecule after sulfite cleavage of XXL Acetaldehyde is formed from pyruvic acid by yeast carboxylase by enzymic cleavage of intermediate XXI, Uberating thiamine pyTophosphate . XXI has also been identified as intermediate in the formation of acetyl-coenzyme A from pyruvic acid by p3u uvic oxidase . The transketolase reaction has been shown to proceed via a gly-colaldehyde-enzyme intermediate here one may expect to find dihydroxy-ethylthiamine pyrophosphate as active glycol-aldehyde . Such experiments strongly support Breslow s concept of the reaction mechanism. 

The studies of Klein and Harris (1938) on different tissues of the rabbit indicated that acetylation was perhaps localized to the liver. Blon-dheim (1955) showed, however, that both red cells and white cells of peripheral blood had the capacity to convert sulfanilamide and p-amino-benzoic acid to their acetylated derivatives. With the development of more sensitive assay techniques making use initially of acetyl coenzyme A generating systems, and later of purified preparations of this cosubstrate, enzymic acetylating activity could be demonstrated in many other mammalian tissues. More recently, tissue distribution studies in animals and man have shown that both the pattern and type of arylamine drug-acety-lating activity varies from one tissue to another within an individual and also between individuals (Hearse and Weber, 1970), in support of pro-... 

Very little is known about the oxidative reactions which lead to the production of acetyl-coenzyme A from fatty acids in animal tissues, but, since it is likely that these oxidations utilize the same electron transfer system as Krebs cycle oxidations, and since fatty acid oxidation takes place in the same enzyme preparations which are used for the study of oxidative phosphorylation, it would seem likely on a priori grounds that the over-all P/0 ratio for fatty acid oxidation must be similar to that observed for the complete oxidation of pyruvate. 

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... 

In the presence of suitable enzymes, which can be prepared from animal tissues or bacteria, acetate becomes reactive, provided that coenzyme A and ATP are present. With these two cofactors and the appropriate enzymes acetate can acetylate sulfanilamide, undergo esterification with choline, or combinefwith oxalacetate to form citrate. Since acetyl coenzyme A is an intermediary in these reactions, one of the main problems concerning the enzymic mechanisms is that of the role of ATP in the synthesis of acetyl coenzyme A. Lynen and Reichert pointed out that it is very unlikely that ATP, acetate, and coenzyme A react together simultaneously, and that the most probable sequence is a primary phosphorylation of coenzyme A by ATP... 

The evidence supporting this concept is derived from experiments on yeast extracts and pigeon liver preparations but further joint studies by Lipmann and Lynen make the formation of phosphoryl-ated or pyrophosphorylated coenzyme A improbable and suggest the formation of enzyme-bound adenosine phosphate and coenzyme A. In the presence of purified yeast enzymes isotopic pyrophosphate was found to exchange the isotope with ATP in the absence of coenzyme A. This excludes the latter as an obligatory participant. Isotopic acetate also exchanged readily with acetyl coenzyme A in the presence of this yeast enzyme. The following scheme of 3 reactions fits the facts ... 

Evidence that acetyl-CoA is the actual active acetate in fungal aromatic biosynthesis was provided by Bassett and Tanenbaum (i960), who showed (a) that coenzyme A could be isolated from the mycelium of P. patulum (b) that radioactive acetyl-CoA, synthesized either from fungal or yeast coenzyme preparations, could be transformed into radioactive patulin by a cell-free extract obtained by the dilute ammonia treatment of mycelial mats. It was also found that biosynthetically-labelled 6-methylsalicylate could be enzymically rearranged to patulin by such extracts. Use of the ammonia extractive procedure followed by partial ammonium sulfate fractionation, gave Lynen and Tada (I96I) an enzyme mixture which synthesized radioactive 6-methylsalicylate from acetyl-1- C-CoA,... 

Acyl-coenzyme A compounds, which, because of their high acetyl group transfer potential represent carriers of activated acyl groups in biological systems, are prepared from the corresponding carboxylic acid, CDI, and coenzyme a.[4h5],[177],[182],[183]... 

Coenzyme A (CoA), 20 249—250. See also Ace to acetyl- Co A in citric acid cycle, 6 633 Coenzyme Q10, 17 673 Coercivity, ofM-type ferrites, 11 70 Coextruded food packaging, 18 44, 45 Coextrusion techniques, for gelatin capsule preparation, 11 549 Cofactors, 10 253 11 4 folic acid, 25 801-802 for enzymes, 3 672-673 protein, 20 828-829 vitamin B12, 25 804 vitamins as, 25 781 Coffea arabica, 7 250 Cojfea Canephora, 7 250 Coffea liberica, 7 250 Coffee, 2 108 6 366 7 250-271 biotechnology, 7 265-267 decaffeinated, 7 263 economic aspects, 7 263-264 estimated maximum oxygen tolerance, 3 381t... 

LADH catalyzes the dismutation of different aldehydes to alcohol and acid in the presence of NAD+ at high aldehyde concentrations (53,347,348). Dalziel and Dickinson (349) found that this reaction did not influence the kinetic parameters of normal aldehyde reduction, provided reasonable substrate concentrations were used. They also suggested a mechanism for the dismutase reaction based on a catalytic role of NAD+. Using acetyl pyridine AD+ instead of NAD+ it could, however, be demonstrated (350) that a net reduction of coenzyme occurs during this reaction. Later studies (351) have shown a stoichiometry of one mole NAD+ reduced per mole acid formed. It was also shown that with octanal as a substrate the reaction exhibits a much higher maximal velocity than with acetaldehyde. The isomerase activity of LADH previously reported (260,352) was later shown to result from impurities in the LADH preparations (353). 

Data which were not available at the time this report was prepared indicate that coenzyme A plays as crucial a role in the metabolism of fatty acids as that of phosphate in carbohydrate metabolism. Lynen (1952, 1953) has described a fatty acid cycle of reversible reactions which can result either in the breakdown of fatty acids to acetyl-CoA or in the synthesis of fatty acids from acetyl-CoA. The reactions can be summarized as follows ... 

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