Fatty Acid Elongation In Mitochondria


Cells typically contain large amounts of C18 and C20 fatty acids. Longer chain fatty acids are found in certain specialized tissues (myelin contains high amounts of C22 and C24 components). Even longer chain fatty acids are derived from either dietary sources or from elongation of C16-CoA or C18-CoA formed by the cytoplasmic fatty acid synthetase system. All of the fatty acids needed by the body can be synthesized from palmitate (C16:0) except the essential, polyunsaturated fatty acids such as linoleate and linolenate. To create longer, shorter, oxidized, reduced fatty acids, palmitic acid is subjected to enzymatic reactions by reductases, hydroxylases, elongases and mixed function oxidases. There are 3 major processes that modify palmitic acid: elongation, desaturation and hydroxylation. Elongation of fatty acids may occur at endoplasmic reticulum where fatty acid molecules of length up to C24 may be produced. Mitochondrial elongation may result in fatty acids up to C16 in length. Fatty acid elongation in mitochondria is essentially the reverse of beta-oxidation for fatty acid oxidation. In particular, both pathways make use of acetyl-CoA acyltransferase, 3-hydroxyacyl-CoA dehydrogenase and enoyl-CoA hydratase. The final step of fatty acid elongation uses enoyl-CoA reductase (not part of the beta-oxidation pathway). The elongation takes place in the mitochondrial matrix. In liver and kidney fatty acid elongation operates best in the presence of both NADH and NADPH, whereas in heart and skeletal muscle, only NADH is required. The mitochondrial pathway is important for elongating fatty acids containing 14 or fewer carbon atoms. Short chain fatty acids (SCFA) are fatty acids with aliphatic tails of less than six carbons. Medium chain fatty acids (MCFA) are fatty acids with aliphatic tails of 6–12 carbons. Long chain fatty acids (LCFA) are fatty acids with aliphatic tails longer than 12 carbons. Very Long chain fatty acids (VLCFA) are fatty acids with aliphatic tails longer than 22 carbons

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References

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