Coenzyme A formation

Egland PG, J Gibson, CS Harwood (1995) Benzoate-coenzyme A ligase, encoded badA, is one of three lighases to catalyze benzoyl-coenzyme A formation during anaerobic growth of Rhodopseudomonas palustris on benzoate. J Bacteriol ill 6545-6551. 

Acetyl coenzyme A, formation, 45 Achlya, sterol utilization, 318,321 Aohlya ambisexualis. growth inhibition, 337 Achlya carolinlana. growth inhibition, 337... 

Grumbach K. and Forn B. 1980. Chloroplast autonomy in acetyl-coenzyme-A formation and terpenoid biosynthesis. Z. Naturforsch. 35c, 645-648. 

Although a variety of oxidizing agents are available for this transformation it occurs so readily that thiols are slowly converted to disulfides by the oxygen m the air Dithiols give cyclic disulfides by intramolecular sulfur-sulfur bond formation An example of a cyclic disulfide is the coenzyme a lipoic acid The last step m the laboratory synthesis of a lipoic acid IS an iron(III) catalyzed oxidation of the dithiol shown... 

Formation of malonyl coenzyme A is followed by a nucleophilic acyl substitution which transfers the malonyl group to the acyl carrier protein as a thioester... 

The four carbon atoms of the butanoyl group originate m two molecules of acetyl coenzyme A Carbon dioxide assists the reaction but is not incorporated into the prod uct The same carbon dioxide that is used to convert one molecule of acetyl coenzyme A to malonyl coenzyme A is regenerated m the decarboxylation step that accompanies carbon-carbon bond formation... 

Carbon-carbon bond formation then occurs between the ketone carbonyl of acetoacetyl coenzyme A and the a carbon of a molecule of acetyl coenzyme A... 

Subsequent knowledge of the stmcture, function, and biosynthesis of the foHc acid coenzyme gradually allowed a picture to be formed regarding the step in this pathway that is inhibited by sulfonamides. The biosynthetic scheme for foHc acid is shown in Figure 1. Sulfonamides compete in the step where condensation of PABA with pteridine pyrophosphate takes place to form dihydropteroate (32). The amino acids, purines, and pyrimidines that are able to replace or spare PABA are those with a formation that requkes one-carbon transfer catalyzed by foHc acid coenzymes (5). 

The fonn in which acetate is used in most of its important biochemical reactions is acetyl coenzyme A (Figure 26.1a). Acetyl coenzyme A is a thioester (Section 20.13). Its formation from pyruvate involves several steps and is summarized in the overall equation ... 

We can describe the major elements of fatty acid biosynthesis by considering the formation of butanoic acid from two molecules of acetyl coenzyme A. The machinery responsible for accomplishing this conversion is a complex of enzymes known as fatty acid synthetase. Certain portions of this complex, refened to as acyl carrier protein (ACP), bear a side chain that is structurally similar to coenzyme A. An important early step in fatty acid biosynthesis is the transfer of the acetyl group from a molecule of acetyl coenzyme A to the sulfhydryl group of acyl canier protein. 

Figure 21.9 Formation of the thioester acetyl CoA by nucleophilic acyl substitution reaction of coenzyme A (CoA with acetyl adenylate.

The sharp flash in the firefly bioluminescence reaction (Fig. 1.6) is due to the formation of a strongly inhibitory byproduct in the reaction. The inhibitor formed is dehydroluciferyl adenylate, having the structure shown below at left. In the presence of coenzyme A (CoA), however, this inhibitory adenylate is converted into dehydroluciferyl-CoA, a compound only weakly inhibitory to luminescence. Thus, an addition of CoA in the reaction medium results in a long-lasting, high level of luminescence (Airth et al., 1958 McElroy and Seliger, 1966 Ford et al., 1995 Fontes et al., 1997, 1998). 

D. Coenzyme A.—Succinyl phosphate (42) reacts rapidly and non-enzymatically with CoA in the pH range 3—8 to yield succinyl CoA (43). This reaction is dependent on the presence of a suitably situated free carboxy-group as such nucleophilic attack at carbon is not known with other acyl phosphates. Moreover, maleyl phosphate reacts rapidly with CoA while fumaryl phosphate fails to react under the same conditions. Hence the formation of a cyclic intermediate (44) from succinyl phosphate is... 

To clarify the characteristics of AMDase, the effects of some additives were examined using phenylmalonic acid as the representative substrate. The addihon of ATP and coenzyme A did not enhance the rate of the reaction, different from the case of malonyl-CoA decarboxylase and others in those, ATP and substrate acid form a mixed anhydride, which in turn reacts with coenzyme A to form a thiol ester of the substrate. In the present case, as both ATP and CoA-SH had no effect, the mechanism of the reaction will be totally different from the ordinary one described above. It is well estabhshed that avidin is a potent inhibitor of the formation of the biotin-enzyme complex. In the case of AMDase, addition of avidin has no influence on the enzyme activity, indicating that AMDase is not a biotin enzyme. 

The acetyl-coenzyme A decarbonylase synthase complex contains five polypeptide sub-nnits and in acetate-degrading methanotrophs, such as Methanosarcina barkeri and M. thermophila, catalyzes the formation of methane and COj from acetyl-CoA ... 

The degradation of vinyl chloride and ethene has been examined in Mycobacterium sp. strain JS 60 (Coleman and Spain 2003) and in Nocardioides sp. strain JS614 (Mattes et al. 2005). For both substrates, the initially formed epoxides underwent reaction with reduced coenzyme M and, after dehydrogenation and formation of the coenzyme A esters, reductive loss of coenzyme M acetate resulted in the production of 5-acetyl-coenzyme A. The reductive fission is formally analogous to that in the glutathione-mediated reaction. 

The degradation of pimelate is initiated by formation of the coenzyme A ester and is followed by a series of steps with the production of glutaryl-CoA that is decarboxylated to crotonyl-CoA... 

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