Regulation of the biosynthesis of 4,7,10,13,16-docosapentaenoic acid
Mohammed, B. Selma
Luthria, Devanand L.
Bakousheva, Svetla P.
B. S. Mohammed, B. S., D. L. Luthria, S. P. Baykousheva, and H. Sprecher, “Regulation of the biosynthesis of 4,7,10,13,16-docosapentaenoic acid,” Biochemical Journal 326 (1997): 425-430.
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It is now established that fatty acid 7,10,13,16-22:4 is metabolized into 4,7,10,13,16-22:5 as follows: 7,10,13,16-22:4!9,12,15,18- 24:4!6,9,12,15,18-24:5!4,7,10,13,16-22:5. Neither C#% fatty acid was esteri®ed to 1-acyl-sn-glycero-3-phosphocholine (1-acyl- GPC) by microsomes, whereas the rates of esteri®cation of 4,7,10,13,16-22:5, 7,10,13,16-22:4 and 5,8,11,14-20:4 were respectively 135, 18 and 160 nmol}min per mg of microsomal protein. About four times as much acid-soluble radioactivity was produced when peroxisomes were incubated with [3-"%C]- 9,12,15,18-24:4 compared with 6,9,12,15,18-24:5. Only [1-"%C]7,10,13,16-22:4 accumulated when [3-"%C]9,12,15,18-24:4 was the substrate, but both 4,7,10,13,16-22:5 and 2-trans- 4,7,10,13,16-22:6 were produced from [3-"%C]6,9,12,15,18-24:5. When the two C#% fatty acids were incubated with peroxisomes, microsomes and 1-acyl-GPC there was a decrease in the production of acid-soluble radioactivity from [3-"%C]6,9,12,15,18-24:5, but not from [3-"%C]9,12,15,18-24:4. The preferential fate of [1-"%C]4,7,10,13,16-22:5, when it was produced, was to move out of peroxisomes for esteri®cation into the acceptor, whereas only small amounts of 7,10,13,16-22:4 were esteri®ed. By using #H-labelled 9,12,15,18-24:4 it was shown that, when 7,10,13,16- 22:4 was produced, its primary metabolic fate was degradation to yield esteri®ed arachidonate. Collectively, the results show that an inverse relationship exists between rates of peroxisomal b-oxidation and of esteri®cation into 1-acyl-GPC by microsomes. Most importantly, when a fatty acid is produced with its ®rst double bond at position 4, it preferentially moves out of peroxisomes for esteri®cation to 1-acyl-GPC by microsomes, rather than being degraded further via a cycle of b-oxidation that requires NADPH-dependent 2,4-dienoyl-CoA reductase.