Cofactors and Chemsitry

Coenzyme A

Chemical structure of Coenzyme A
Usually denoted as "CoA" or "CoA-SH". Where the "-SH" indicates the thiol at the end. The coenzyme can be divided into three parts as noted above: ADP, Panthothenic Acid (vitamin B5) and β-Mercaptoethylamine. The Sulfur on the end is the active portion involved in chemistry.		 3D representation of CoA

Vitamin B5 Dependence: Humans do not synthesize Pantothenic Acid (the middle portion of CoA) and therefore require its intake as part of the diet. Pantothenic Acid is one of the (many) B types typically called vitamin B5. You may read much more about this and issues regarding its synthesis and deficiencies here.

Coenzyme A is involved in many reactions including transport and synthesis. Its primary role in synthesis is to "activate" the α-carbon of an orgainic acid. This can allow C-C bond formation or even elimination of 2 H across the α-β carbon bond.
CoA can be used to "activate" acyl groups (acetic acid) by making a thioester between the S of CoA and the organic acid. This allows the acid to "act" like a ketone and allows electrons to more freely on the double bonded oxygen. The end result is that it allows the adjoining of acetyl groups into fatty acids or allows the desaturation of a fatty acid.

Here Coenzyme A is required for the Flavin dependent desaturation of a fatty acid.

Here Coenzyme A is required to "activate" the acetyle group so that it can make a C-C bond to another acetyl CoA. This can still be considered an Aldol Reaction since the thioester is acting a a ketone - as mentioned above.
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SOME ENZYMES USING THIS COFACTOR
Citrate synthase This enzyme is part of the Krebs cycle. We will learn much more about this enzyme in module 7
Pyruvate Dehydrogenase This is enzyme is an important "adpater" between glycolysis and the Krebs cycle. We will learn about this in Module 6.