Fatty acids and their CoA byproducts can be found in many places in the body, playing major roles in many basic functions of the body. These include signalling roles, energy creation roles and enzyme regulation. Beta-oxidation is a process that occurs in the peroxisomes and in the mitochondria, although this pathway is focused on the mitochondrial piece of that process. Depending on the length of the fatty acid, beta-oxidation will either begin in the peroxisomes or the mitochondria. Very long chain fatty acids, fatty acids that consist of more than 22 carbons, can be reduced in the peroxisome where they become octanyl-CoA before moving to the mitochondria for the rest of the oxidation process. Stearoylcarnitine is transported by a mitochondrial carnitine/acylcarnitine carrier protein into the mitochondrial matrix, where it is converted to stearoyl-CoA through the enzyme carnitine o-palmitoyltransferase 2. Stearoyl-CoA then is catalyzed into (2E)-octadecenoyl-CoA by the enzyme long-chain specific acyl-CoA dehydrogenase. Then, enoyl-CoA hydratase converts (2E)-octadecenoyl-CoA into (s)-hydroxyoctadecanoyl-CoA. The pathway continues as hydroxyacyl-coenzyme A dehydrogenase cleaves (s)-hydroxyoctadecanoyl-CoA into 3-oxooctadecanoyl-CoA. 3-oxooctadecanoyl-CoA then uses 3-ketoacyl-CoA thiolase to create acetyl-CoA (necessary for the citric acid cycle) and uses trifunctional enzyme subunits alpha and beta to create palmityl-CoA. This palmityl-CoA is then converted by long-chain specific acyl-CoA dehydrogenase to (2E)-hexadecenoyl-CoA. Enoyl-CoA then converts (2E)-hexadecenoyl-CoA to 3-hydroxyhexadecanoyl-CoA, which is then turned into 3-oxohexadecanoyl-CoA by the enzyme hydroxyacyl-coenzyme A dehydrogenase. 3-ketoacyl-CoA thiolase then creates acetyl-CoA with the help of trifunctional enzyme subunits alpha and beta, which also produce tetradecanoyl-CoA from 3-oxohexadecanoyl-CoA. Long-chain specific acyl-CoA dehydrogenase then converts tetradecanoyl-CoA to (2E)-tetradecenoyl-CoA. (2E)-tetradecenoyl-CoA is then converted by the enzyme enoyl-CoA hydratase into 3-hydroxytetradecanoyl-CoA, which then creates 3-oxotetradecanoyl-CoA through the enzyme hydroxyacyl-coenzyme A dehydrogenase. Finally, the 3 enzymes 3-ketoacyl-coA thiolase, trifunctional enzyme subunit alpha and trifunctional enzyme subunit beta convert 3-oxotetradecanoyl-CoA into acetyl-CoA and lauroyl-CoA which can then be beta-oxidized as medium chain saturated fatty acids.

Mitochondrial Beta-Oxidation of Long Chain Saturated Fatty Acids References