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Coenzyme A

Coenzyme A is a prominent coenzyme of living organisms which transfer the acyl group of carboylic acids. This is abbreviated as CoA, where A stands for acylation. The structure of this coenzyme was established by Lipmann and Snell in 1940 and its laboratory synthesis was elucidated by Khorana in 1959. The chemical structure of coenzyme A is complex and it is derived from pantothenic acid, a growth factor of many microorganisms.

Pantothenic acid has widespread distribution and is identified as a γ-dihydroxy-β, β-dimethylbutyryl- β-alanine: 

pantothemic acid

Deficiency of this vitamin in man causes burning feet in patients suffering from beri-beri and pellagra. The best sources for this vitamin are liver, kidney, meat, bran, peas and yeast.
A coenzyme A can be divided into two components , adenosine 3, 5 – diphosphate and pantothenic, which is formed by combination of pantothenic acid with mercaptoethylamine.

Biochemical function  The coenzyme A or CoA-SH (CoA) gives rise to acy –CoA derivatives which are formed generally in ATP-dependent synthetase reactions, called thioesters in chemical terms. These thioesters are ighly reactive and percolate in various types of reaction involving (a) nucleophilic attack at the acyl carbon atom, (b) addition to unsaturated acyl derivatives of CoA-SH, (c) condensation at the α-carbon of the acyl-SCoA, and (d) acyl group intercharge.

 (a)    In the first category, there is nucleophilic attack on the α -carbon atom and the acyl function is transferred with the release of CoA-SH. This is shown by the following reactions:

sturcuture of conenzyme A (CoA -SH)

(b)    In this group of reaction, addition of water to unsaturated acyl derivatives takes place to form L-β-hydroxylacyl-S CoA derivatives

L -b hydroxylacyl -s coa derivatives
 (c)   These reactions generally occur with carbonyl groups involving condensation at theα-carbon atom which receives a partial negative charge from the coenzyme.

oxaloacetate and citrate

(d)    Reactions involving interchange of acyl groups:

Reaction invloving interchange of acyl groups.

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