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).
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