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Can the oxidation of pyruvate to acetyl coa be called as acetylation in some ways? Please include credible sources in the answer.

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    $\begingroup$ Acetylation means addition of an acetyl (CH₃CO-) group, not formation of acetate. Pyruvate to Ac-CoA is quite a complex reaction. Please try to do some prior research before asking. The objective of your question is unclear. $\endgroup$ – WYSIWYG Apr 4 '17 at 8:59
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Acetylation is defined as1:

Acetylation (or in IUPAC nomenclature ethanoylation) describes a reaction that introduces an acetyl functional group into a chemical compound.

So, any reaction in which an acetyl (CH3CO-) group adds to another compound is an acetylation reaction. A common example is Friedel-Crafts acetylation reaction:

friedel-crafts acylation

If the reaction is catalyzed by pyruvate dehydrogenase: In this case, first of all the reaction that you refer to is termed as pyruvate decarboxylation (rather than oxidation, although it won't hurt either). As @WYSIWYG has said in comments, it is not a simple reaction, it involves three steps (+ 2 steps for regeneration of complex), each catalyzed by different enzymes. The name given for the whole complex is pyruvate dehydrogenase complex (PDC)2. The steps involved are3:

  1. The keto carbon of pyruvate reacts with the carbanion of TPP on E1 to yield an addition compound. The electron-pulling positively charged nitrogen of the thiazole ring promotes loss of CO2. What remains is hydroxyethyl-TPP.

  2. The hydroxyethyl carbanion on TPP of E1 reacts with the disulfide of lipoamide on E2. What was the keto carbon of pyruvate is oxidized to a carboxylic acid, as the disulfide of lipoamide is reduced to a dithiol. The acetate formed by oxidation of the hydroxyethyl moiety is linked to one of the thiols of the reduced lipoamide as a thioester.

  3. The acetate is transferred from the thiol of lipoamide to the thiol of coenzyme A, yielding acetyl CoA.

pyruvate dehydrogenase mechanism

Now, pyruvic acid has the formula: $CH_3-CO-COOH$. So, if you look at the step C of reaction, then since CH3CO- has been added to coenzyme A, hence, in a way, it would be considered an acetylation reaction. Pay attention that the complete reaction will not be considered acetylation, only a part of it would be. This is also the reason why calling the complete reaction as oxidation won't hurt, because even decarboxylation is just a part of complete reaction.

If the reaction is not catalyzed by pyruvate dehydrogenase Taking the question out from pyruvate dehydrogenase (as you don't talk specifically about that), there is an enzyme Acetyl-coA synthetase whose job is catalyzing acetylation of coenzyme-A(!)4. The reaction looks like this:

$ATP + acetate + co-A \rightarrow AMP + pyrophosphate + acetyl-coA$

The enzyme is of two types: AMP forming and ADP forming5:

acetyl-coA synthetase mechanism

So, as long as the conversion is not one specifically catalyzed by pyruvate dehydrogenase, we can say that Yes, conversion of coenzyme-A to Acetyl-coA is an acetylation reaction.

References:

  1. Acetylation - Wikipedia

  2. Pyruvate Dehydrogenase - Wikipedia

  3. Pyruvate Dehydrogenase and Krebs Cycle - Joyce J. Diwan; Rensselaer Polytechnic Institute

  4. Acetyl-coA synthetase - Wikipedia

  5. Hentchel KL, Escalante-Semerena JC. 15 July 2015. Acylation of biomolecules in prokaryotes: a widespread strategy for the control of biological function and metabolic stress. Microbiol Mol Biol Rev doi:10.1128/MMBR.00020-15

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    $\begingroup$ I would only regard the CoA-SH to A-CoA being the acetylation step. Otherwise the full glycolysis pathway could be called an acetylation reaction - hardly true isn't it? $\endgroup$ – AliceD Apr 4 '17 at 10:16
  • $\begingroup$ I (accidentally) wrote the word acetylation while explaining about that reaction in my exam. It's only a part of a part of aquestion but if my instructor marks some of the points off, can I say that "it has acetylation in the process so its technically correct"? Both acetylation and decarboxylation are not stated in my textbook. Can I also say that acetylation IS oxidation? Sorry if it was too personal. I thought it was worthy enough to discuss the aspects here $\endgroup$ – user31285 Apr 4 '17 at 11:31
  • $\begingroup$ The pyruvate dehydrogenase complex catalyzes the oxidative decarboxylation of pyruvate to acetyl-CoA and CO2, where the oxidative step is more correctly a dehydrogenation (and where pyruvate is the source of the electrons) . How can this possible not be an acetylation reaction, or in any way violate the IUPAC definition you quote? . $\endgroup$ – user1136 Apr 4 '17 at 11:40
  • $\begingroup$ @denniskim There is difference between acetylation and oxidation. Also, (assuming you're in high school where this is a single step conversion), you can say that its technically correct. You can discuss general concepts here, but personal exam questions are off-topic here. $\endgroup$ – another 'Homo sapien' Apr 4 '17 at 11:52
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    $\begingroup$ @DennisKim I think the right way to think about it is this: most reactions operate on more than one molecule. In the case of pyruvate dehydrogenase, the reaction is decarboxylation of pyruvate and concomitant acetylation of CoA. (The decarboxylation steps is oxidative, so you could also call that part oxidation). Most people focus on what happens to the pyruvate, but as explained by many answers above, you can't have one without the other. $\endgroup$ – Victor Chubukov Apr 4 '17 at 13:56