Palmitoyl-CoA is an acyl-CoA thioester. It is an "activated" form of palmitic acid and can be transported into the mitochondrial matrix by the carnitine shuttle system (which transports fatty acyl-CoA molecules into the mitochondria), and once inside can participate in beta-oxidation. Alternatively, palmitoyl-CoA is used as a substrate in the biosynthesis of sphingosine (this biosynthetic pathway does not require transfer into the mitochondria).[1][2]
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| Names | |
|---|---|
| IUPAC name 3′-O-Phosphonoadenosine 5′-{(3R)-4-[(3-{[2-(hexadecanoylsulfanyl)ethyl]amino}-3-oxopropyl)amino]-3-hydroxy-2,2-dimethyl-4-oxobutyl dihydrogen diphosphate} | |
| Systematic IUPAC name O1-{[(2R,3S,4R,5R)-5-(6-Amino-9H-purin-9-yl)-4-hydroxy-3-(phosphonooxy)oxolan-2-yl]methyl} O3-{(3R)-4-[(3-{[2-(hexadecanoylsulfanyl)ethyl]amino}-3-oxopropyl)amino]-3-hydroxy-2,2-dimethyl-4-oxobutyl} dihydrogen diphosphate | |
| Identifiers | |
3D model (JSmol) | |
| ChemSpider | |
| ECHA InfoCard | 100.015.616 |
| KEGG | |
| MeSH | Palmitoyl+Coenzyme+A |
PubChem CID | |
CompTox Dashboard (EPA) | |
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| Properties | |
| C37H66N7O17P3S | |
| Molar mass | 1005.95 g·mol−1 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
Biosynthesis
Palmitoyl CoA formed from palmitic acid, in the reaction below.[3]
- Palmitate + CoA-SH + ATP → Palmitoyl-CoA + AMP + Pyrophosphate
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.[4] The reaction is driven to completion by the exergonic hydrolysis of pyrophosphate.[3]
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:
- Palmitoyl-CoA + Carnitine ⇌ Palmitoyl-Carnitine + CoA-SH
This transesterification reaction is catalyzed by carnitine palmitoyl transferase.[5] 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 H+, and 7 FADH2.[6] The full reaction is below:
- Palmitoyl-CoA + 7 CoA-SH + 7 NAD+ + 7 FAD → 8 Acetyl-CoA + 7 NADH + 7 H+ + 7 FADH2
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.[7]
Sphingosine synthesis
Additional images
Synthesis
See also
- Coenzyme A (CoA)