Coenzyme A (often abbreviated as CoA, CoASH, or HSCoA) is a coenzyme, notable for its role in the synthesis and oxidation of fatty acids, and the oxidation of pyruvate in the citric acid cycle. All sequenced genomes encode enzymes that use Coenzyme A as a substrate, underscoring its universal importance to biological cells.
Structurally, Coenzyme A is a thiol, meaning it contains a sulfhydryl group (-SH). This thiol group is the active part of the molecule where acyl groups (derived from acids by removal of a hydroxyl group) are attached by thioester bonds, forming acyl-CoA derivatives. The rest of the CoA molecule serves as a handle by which the acyl group is carried through metabolic reactions.
The molecule consists of an adenosine diphosphate (ADP), a pantothenic acid (a vitamin belonging to the B5 class), and a thiol group. The synthesis of Coenzyme A starts with pantothenate (vitamin B5) and involves several enzymatic steps, including the addition of cysteine and the formation of the thiol group that is critical for its activity.
Coenzyme A is central to the metabolism of carbohydrates, amino acids, and lipids. It plays a key role in the citric acid cycle (also known as the Krebs cycle or TCA cycle), which is a fundamental metabolic pathway that produces energy from the oxidation of glucose, fats, and proteins. In the TCA cycle, CoA is involved in the conversion of pyruvate to acetyl-CoA, which then enters the cycle and is oxidized for energy production.
Furthermore, CoA is involved in the biosynthesis of many important compounds, including the synthesis of fatty acids, where it carries acyl groups, and the oxidation of fatty acids in the process known as β-oxidation. In β-oxidation, fatty acids are broken down, generating acetyl-CoA, which can then enter the citric acid cycle.
Coenzyme A's role is not limited to energy metabolism; it also participates in the synthesis of cholesterol, detoxification pathways in the liver, and the synthesis of acetylcholine, an important neurotransmitter. Its ubiquitous presence and multifunctional roles make it essential to life, highlighting the complexity and interconnectivity of metabolic pathways in biological systems.