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Propionyl-CoA

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Title: Propionyl-CoA  
Author: World Heritage Encyclopedia
Language: English
Subject: Methionine, Methylmalonyl-CoA, Propionyl-CoA carboxylase, Beta-Hydroxybutyryl-CoA, Crotonyl-CoA
Collection: Metabolism, Thioesters of Coenzyme A
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Propionyl-CoA

Propionyl-CoA
Identifiers
CAS number  N
PubChem
ChemSpider  YesY
MeSH
Jmol-3D images Image 1
Properties
Molecular formula C24H40N7O17P3S
Molar mass 823.60 g/mol
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N   YesY/N?)

Propionyl-CoA is a coenzyme A derivative of propionic acid.

Contents

  • Metabolism in animals 1
    • Production 1.1
    • Metabolic fate 1.2
  • Metabolism in plants and insects 2
  • References 3

Metabolism in animals

Production

There are several different ways in which it is formed:

Metabolic fate

In mammals, propionyl-CoA is converted to (S)-methylmalonyl-CoA by propionyl-CoA carboxylase, a biotin-dependent enzyme also requiring bicarbonate and ATP.

This product is converted to (R)-methylmalonyl-CoA by methylmalonyl-CoA racemase.

(R)-Methylmalonyl-CoA is converted to succinyl-CoA, an intermediate in the tricarboxylic acid cycle, by methylmalonyl-CoA mutase, an enzyme requiring cobalamin to catalyze the carbon-carbon bond migration.

The methylmalonyl-CoA mutase mechanism begins with the cleavage of the bond between the 5' CH2- of 5'-deoxyadenosyl and the cobalt, which is in its 3+ oxidation state (III), which produces a 5'-deoxyadenosyl radical and cabalamin in the reduced Co(II) oxidation state.

Next, this radical abstracts a hydrogen atom from the methyl group of methylmalonyl-CoA, which generates a methylmalonyl-CoA radical. It is believed that this radical forms a carbon-cobalt bond to the coenzyme, which is then followed by the rearrangement of the substrate's carbon skeleton, thus producing a succinyl-CoA radical. This radical then goes on to abstract a hydrogen from the previously produced 5'-deoxyadenosine, again creating a deoxyadenosyl radical, which attacks the coenzyme to reform the initial complex.

A defect in methylmalonyl-CoA mutase enzyme results in methylmalonic aciduria, a dangerous disorder that causes a lowering of blood pH.

Metabolism in plants and insects

In plants and insects propionyl-CoA is metabolized to acetate in a very different way, similar to beta-oxidation.

Not all details of this pathway have been worked out, but it appears to involve formation of acrylyl-CoA, then 3-hydroxypropionyl-CoA.

This is metabolized with loss of carbon 1 of 3-hydroxypropionyl-CoA as carbon dioxide, while carbon 3 becomes carbon 1 of acetate.

References

  • Halarnkar P, Blomquist G (1989). "Comparative aspects of propionate metabolism". Comp. Biochem. Physiol., B 92 (2): 227–31.  
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