Coenzyme A

Figure 1. Coenzyme A.

Coenzyme A (CoA, CoASH or HSCoA) is the key cofactor in first step of the TCA cycle, responsible for transferring the acetyl group from pyruvate oxidation to oxaloacetate yielding citrate.

Coenzyme A is also a critical cofactor in fatty acid metabolism. Coenzyme A carries fatty acids through the catabolic/oxidation process in the mitochondria and transfers acetyl groups during the elongation process of fatty acid synthesis in the cytosol.

The acetyl moiety of acetylCoA is bound by a high-energy bond (free energy 34.3 kJ/mol) to the -SH group of Coenzyme A. It is also a precursor to, steroids and other naturally occurring compounds, such as terpenes and acetogenins present in plants.^1,2

In the transfer reaction by Acetyl CoA of the C2 acetyl fragment, either the carboxyl group or the methyl group may react (electrophilic vs. nucleophilic reaction, respectively).²

AcetylCoA is prepared enzymatically by reacting Coenzyme A with Acetyl Phosphate and Phosphotransacetylase. The product is purified by ion exchange chromatography. Several methods of preparation and methods for the determination of Acetyl CoA and other CoA derivatives have been described in the literature.^3,4,5 Coenzyme A is synthesized in vivo from pantothenate, cysteine, and adenosine. Pantothenate is phosphorylated, joined with cysteine, decarboxylated, joined with adenosine and phosphorylated again to the 3’ ribose position to yield Coenzyme A.¹