Reevaluation of the pathways for the biosynthesis of polyunsaturated fatty acids

9,12,15,18,21-24:5-->6,9,12,15,18,21-24:6 4,7,10,13,16,19-22:6. The synthesis of 4,7,10,13,16-22:5 from 7,10,13,16-22:4 takes place via an analogous pathway. According to these pathways the 24-carbon acids that are made in the endoplasmic reticulum move to a site for partial beta-oxidation, which is most likely peroxisomes. The products of partial beta-oxidation, 4,7,10,13,16-22:5 and 4,7,10,13,16,19-22:6, then move back to the endoplasmic reticulum where they are used as substrates for membrane lipid biosynthesis. The ability of a fatty acid to serve as a substrate for continued peroxisomal beta-oxidation, versus its transfer out of peroxisomes for subsequent endoplasmic reticulum-associated esterification reactions, may be an important control for regulating membrane lipid fatty acid composition. Indeed, the revised pathways of polyunsaturated fatty acid biosynthesis imply that there is considerable intracellular movement and recycling of fatty acids between peroxisomes and the endoplasmic reticulum. In addition, these revised pathways require that two 18-carbon and two 24-carbon acids are substrates for desaturation at position 6. Also, as linoleate and linolenate are metabolized, respectively, to 6,9,12,15,18-24:5 and 6,9,12,15,18,21-24:6, three n-6 acids and three n-3 acids are substrates for malonyl-CoA dependent chain elongation. It remains to be determined how many microsomal enzymes are required to carry out these reactions and whether other ancillary enzymes are expressed in tissues whose membrane lipids accumulate very long-chain polyunsaturated acids with up to 36 carbon atoms. -->
Jazyk: English
ISSN: 0022-2275
Přístupová URL adresa: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::d0b3d2baa06774a8c60fed12adf705dd
http://www.sciencedirect.com/science/article/pii/S0022227520410843
Rights: OPEN
Přírůstkové číslo: edsair.doi.dedup.....d0b3d2baa06774a8c60fed12adf705dd
Autor: Svetla P. Baykousheva, B. S. Mohammed, Devanand L. Luthria, Howard Sprecher
Jazyk: angličtina
Rok vydání: 1995
Předmět:
Zdroj: Journal of Lipid Research, Vol 36, Iss 12, Pp 2471-2477 (1995)
Scopus-Elsevier
ISSN: 0022-2275
Popis: Recent studies refute the commonly accepted, but untested, hypothesis that 7,10,13,16-22:4 and 7,10,13,16,19-22:5 are desaturated at position 4 by a microsomal acyl-CoA-dependent desaturase. The synthesis of 4,7,10,13,16,19-22:6 occurs via the following reaction sequence: 7,10,13,16,19-22:5-->9,12,15,18,21-24:5-->6,9,12,15,18,21-24:6 4,7,10,13,16,19-22:6. The synthesis of 4,7,10,13,16-22:5 from 7,10,13,16-22:4 takes place via an analogous pathway. According to these pathways the 24-carbon acids that are made in the endoplasmic reticulum move to a site for partial beta-oxidation, which is most likely peroxisomes. The products of partial beta-oxidation, 4,7,10,13,16-22:5 and 4,7,10,13,16,19-22:6, then move back to the endoplasmic reticulum where they are used as substrates for membrane lipid biosynthesis. The ability of a fatty acid to serve as a substrate for continued peroxisomal beta-oxidation, versus its transfer out of peroxisomes for subsequent endoplasmic reticulum-associated esterification reactions, may be an important control for regulating membrane lipid fatty acid composition. Indeed, the revised pathways of polyunsaturated fatty acid biosynthesis imply that there is considerable intracellular movement and recycling of fatty acids between peroxisomes and the endoplasmic reticulum. In addition, these revised pathways require that two 18-carbon and two 24-carbon acids are substrates for desaturation at position 6. Also, as linoleate and linolenate are metabolized, respectively, to 6,9,12,15,18-24:5 and 6,9,12,15,18,21-24:6, three n-6 acids and three n-3 acids are substrates for malonyl-CoA dependent chain elongation. It remains to be determined how many microsomal enzymes are required to carry out these reactions and whether other ancillary enzymes are expressed in tissues whose membrane lipids accumulate very long-chain polyunsaturated acids with up to 36 carbon atoms.
Databáze: OpenAIRE
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