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Incorporation into lipid classes of products from microsomal desaturation of isomeric trans ‐octadecenoic acids
Author(s) -
Riisom T.,
Holman R. T.
Publication year - 1981
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/bf02535059
Subject(s) - chemistry , phosphatidylcholine , microsome , phospholipid , phosphatidylethanolamine , isomerization , stereochemistry , double bond , composition (language) , chromatography , biochemistry , organic chemistry , enzyme , linguistics , philosophy , membrane , catalysis
The microsomal desaturation of positional isomers of trans ‐octadecenoic acids is effected by the Δ9‐desaturase and, with concomitant geometric isomerization, cis,trans ‐ and cis,cis ‐octadecadienoic acids of unusual structure are formed. Incorporation of the substrates and their products into lipids varied from 50.5% for incubations with 14–18∶1 to 81.0% for 6–18∶1. A detailed study of the composition of each of the major lipid classes, i.e., phospholipids, triacylglycerol and cholesteryl esters, as well as the composition of the free fatty acid fraction, revealed a complex picture. Generally, the c,c ‐18∶2 products were enriched in the phospholipid fraction, whereas the c,t ‐18∶2 appeared preferentially in cholesteryl esters. The 18∶1 substrates themselves did not show marked preferences for any of the lipid classes. Phospholipase A 2 action on phosphatidylcholine and phosphatidylethanolamine demonstrated enrichment of the c,c ‐ and the c,t ‐18∶2 products in the 2‐position, whereas the 18∶1 substrates were preferentially inserted into the 1‐positions. The c,c ‐ and c,t ‐18∶2 formed by desaturation of t 11–18∶1 varied from this pattern, probably due to their conjugated double bond structures. Linoleic acid, c 9, c 12–18∶2, formed during desaturation of t 12–18∶1, surprisingly showed enrichment in the 1‐position of phosphatidylcholine. Incubation experiments with t 5‐ and t 6‐isomers using liver microsomes from rats fed a corn‐oil‐supplemented diet showed conversion and incorporation rates similar to the rates obtained with microsomes from EFA‐deficient rats. The fatty acid composition of lipid classes and the distributions of products and substrate between the 1‐ and 2‐positions of phosphatidylcholine also agreed with results obtained using microsomes from EFA‐deficient rats.