Palmitoyl-CoA

Biosynthesis

Palmitoyl CoA formed from palmitic acid, in the reaction below.

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This reaction is often referred to as the "activation" of a fatty acid. The activation is catalyzed by palmitoyl-coenzyme A synthetase and the reaction proceeds through a two step mechanism, in which palmitoyl-AMP is an intermediate. The reaction is driven to completion by the exergonic hydrolysis of pyrophosphate.

The activation of fatty acids occurs in the cytosol and beta-oxidation occurs in the mitochondria. However, long chain fatty acyl-CoA cannot cross the mitochondrial membrane. If palmitoyl-CoA is to enter the mitochondria, it must react with carnitine in order to be transported across:

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This transesterification reaction is catalyzed by carnitine palmitoyl transferase. Palmitoyl-Carnitine may translocate across the membrane, and once on matrix side, the reaction proceeds in reverse as CoA-SH is recombined with palmitoyl-CoA, and released. Unattached carnitine is then shuttled back to the cytosolic side of mitochondrial membrane.

Beta-oxidation

Once inside the mitochondrial matrix, palmitoyl-CoA may undergo β-oxidation. The full oxidation of palmitic acid (or palmitoyl-CoA) results in 8 acetyl-CoA's, 7 NADH, 7 , and 7 FADH2. The full reaction is below:

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Sphingolipid biosynthesis

Palmitoyl-CoA is also the starting substrate, along with serine, for sphingolipid biosynthesis. Palmitoyl CoA and serine participate in a condensation reaction catalyzed by serine C-palmitoyltransferase (SPT), in which 3-ketosphinganine is formed. These reactions occur in the cytosol.

:[[Image:Sphingosine synthesis corrected.png|thumb|left|600px|Sphingosine synthesis]]

Additional images

Image:Sphk1 diag b.jpg|Synthesis Image:Palmitic acid.png|Palmitic acid Image:Coenzym A.svg|Coenzyme A

References

References

1. (1969). "Biosynthesis of sphingolipid bases. 3. Isolation and characterization of ketonic intermediates in the synthesis of sphingosine and dihydrosphingosine by cell-free extracts of ''Hansenula ciferri''". J. Biol. Chem..
2. (1968). "Biosynthesis of dihydrosphingosine in vitro". Hoppe-Seyler's Z. Physiol. Chem..
3. (2016-02-29). "Fundamentals of Biochemistry: Life at the Molecular Level". John Wiley & Sons.
4. (1973-02-01). "Palmitoyl-coenzyme A synthetase. Mechanism of reaction". Biochemical Journal.
5. Sharma, R.. (2013). "Bioactive Food as Dietary Interventions for Liver and Gastrointestinal Disease". Elsevier.
6. (2017). "Ketoacidosis". Elsevier.
7. (1997-10-20). "Conversion of dihydroceramide to ceramide occurs at the cytosolic face of the endoplasmic reticulum". FEBS Letters.