Pantothenic acid (vitamin B5) is an important cofactor involved in cell metabolism of carbohydrates, fats and proteins. The vitamin belongs to the group of vitamin B-complexes which are all water soluble. It occurs primarily bound as part of coenzyme A (CoA) where it is known as pantothenic acid. When bound to the acyl carrier protein (ACP) it is known as pantothenol. It is also found in its free acid form in tissues. All these coenzymes have a role in mediating the many critical cell reactions required for intermediary metabolism. It acts primarily through an active sulphydryl group which are controlled by specific steric characteristics of the central pantothenate structure.
The vitamin is produced synthetically because it is unstable. It is added to formulations as calcium pantothenate. It is an oily, yellow liquid, hygroscopic which means it picks up water easily and readily dissolves in water.
Pantothenic acid is very widespread in nature. The stem of its name is from the Greek ‘panthos‘, meaning everywhere. Rich sources of this vitamin occur in meat, legumes like beans and peas, eggs, various fruit and vegetables.
The daily recommended dose based on RDA has not yet been established. A daily dose of 4 to 7 mg for adults and 3- 4 mg for adolescents are usually recommended.
Conditions where vitamin B5 deficiency occur are known as hypovitaminosis. Whilst deficiency is rare, there are certain medical conditions where general vitamin intake and absorption is compromised.
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Synthesis Of Coenzyme A In the Body
The synthesis of coenzyme A in cells takes place in five steps:
1. Pantothenate kinase (PanK, CoaA, CoaX) initiates the phosphorylation of pantothenic acid (vitamin B5) in 4′-phosphopantatenate.
2. The following enzyme phosphopantotenoylcysteine synthetase (PPC-DC; CoaB) adds one cysteine molecule and 4′-phospho-N-pantothenilcysteine (PPC) is produced.
3. 4′-phospho-N-pantothenylcysteine is decarboxylated and converted into 4′-phosphopantetein. This reaction is catalyzed by the enzyme, phosphopentothiocystic decarboxylase (CoaC).
4. Enzymes of phosphopantetein adenyl transferase (CoaD) add one adenyl group to form dephosphorylated coenzyme A (dephospho-CoA).
5. In the final reaction, phosphorylation of dephospho-CoA in coenzyme A occurs by the enzyme defosfocus-A kinase (CoAE). The source of phosphate groups in this step is ATP.