Coenzyme A may act as an acyl group carrier to form acetyl-CoA and other related compounds; this is a way to transport carbon atoms within the cell.
The transfer of carbon atoms by coenzyme A is important in cellular respiration, as well as the biosynthesis of many important compounds such as fatty acids, cholesterol, and acetylcholine.
Biosynthesis
Coenzyme A is synthesized in a five-step process from pantothenate:
1. Pantothenate is phosphorylated to 4’-phosphopantothenate by the enzyme pantothenate kinase
2. A cysteine is added to 4’-phosphopantothenate by the enzyme phosphopantothenoylcysteine synthetase to form 4’-phospho-N-pantothenoylcysteine (PPC)
3. PPC is decarboxylated to 4’-phosphopantetheine by phosphopantothenoylcysteine decarboxylase
4. 4’-phosphopantetheine is adenylylated to form dephospho-CoA by the enzyme phosphopantetheine adenylyl transerase
5. Finally, dephospho-CoA is phosphorylated using ATP to coenzyme A by the enzyme dephosphocoenzyme A kinase.
Acyl group carrier
Since coenzyme A is chemically a thiol, it can react with carboxylic acids to form thioesters, thus functioning as an acyl group carrier.
It assists in transferring fatty acids from the cytoplasm to mitochondria. A molecule of coenzyme A carrying an acetyl group is also referred to as acetyl-CoA. When it is not attached to an acyl group it is usually referred to as ’CoASH’ or ’HSCoA’.
citric acid cycle
Acetyl-CoA is used in the condensation of oxaloacetate to citrate at the initiation of the citric acid cycle (TCA cycle or Krebs cycle).
fatty acid biosynthesis
From the citric acid cycle, acetyl-CoA can also initiate the fatty acid synthesis pathway.
Coenzyme A activated acyl groups
Acetyl-CoA
Propionyl-CoA
Acetoacetyl-CoA
Coumaroyl-CoA (used in flavonoid and stilbenoid biosynthesis)
Acyl derived from dicarboxylic acids
- Malonyl-CoA
- Succinyl-CoA
- Hydroxymethylglutaryl-CoA (used in isoprenoid biosynthesis)
- Pimelyl-CoA (used in biotin biosynthesis)
Butyryl CoA
Pathology
pantothenic acid deficiency (vitamin B5)
- Pantothenic acid is used in the synthesis of coenzyme A (CoA). Since pantothenic acid participates in a wide array of key biological roles, it is considered essential to all forms of life. As such, deficiencies in pantothenic acid may have numerous wide-ranging effects.
See also
citric acid cycle
fatty acid beta oxidation
cholesterol biosynthesis