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Reevaluation of the Pathway for the Metabolism of 7,10,13, 16-docosatetraenoic Acid to 4,7,10,13,16-docosapentaenoic Acid in Rat Liver

Reevaluation of the Pathway for the Metabolism of 7,10,13, 16-docosatetraenoic Acid to 4,7,10,13,16-docosapentaenoic Acid in Rat Liver

B S Mohammed, S Sankarappa, M Geiger, H Sprecher

Arch Biochem Biophys. 1995 Feb 20;317(1):179-84.

PMID: 7872781

Abstract:

When rat liver microsomes were incubated with [1-14C]22:4(n-6) under standard conditions for measuring acyl-CoA desaturases, it was not possible to detect the synthesis of any 22:5(n-6). When malonyl-CoA and NADPH were included in the incubation, 22:4(n-6) was chain elongated to 24:4(n-6), which was then desaturated to 24:5(n-6). Rat hepatocytes metabolized [1-14C]22:4(n-6), [3-14C]24:4(n-6), and [3-14C]24:5(n-6) to yield esterified radioactive 22:5(n-6). The results show that 22:4(n-6) is the precursor of 22:5(n-6) but the pathway is independent of an acyl-CoA-dependent 4-desaturase and probably requires intracellular communication between the endoplasmic reticulum and a site for beta-oxidation. Microsomal reaction rates for (n-6) versus (n-3) polyunsaturated fatty acid biosynthesis cannot per se be used to explain why in vivo most membrane lipids preferentially accumulate 22:6(n-3) rather than 22:5(n-6). Rates of desaturation of 24:4(n-6) and 24:5(n-3) at position 6 were similar (M. Geiger et al., Biochim. Biophys. Acta 1170, 137-142, 1993). We now show that 20:4(n-6) and 20:5(n-3) are chain elongated at the same rate as are 22:4(n-6) and 22:5(n-3). At present, no single reaction can be defined as being substrate specific or rate limiting to explain why there is an apparent selective synthesis and acylation of 22:6(n-3) rather than 22:5(n-6) into membrane lipids.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP25182745	all-cis-4,7,10,13,16-Docosapentaenoic acid		25182-74-5	Price

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