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The questionable role of a microsomal °8 acyl‐CoA‐dependent desaturase in the biosynthesis of polyunsaturated fatty acids
Author(s) -
Chen Qi,
Yin Feng Qin,
Sprecher Howard
Publication year - 2000
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/s11745-000-0596-9
Subject(s) - arachidonic acid , endogeny , chemistry , microsome , biochemistry , clinical chemistry , polyunsaturated fatty acid , fatty acid , biosynthesis , lipidology , linoleic acid , substrate (aquarium) , enzyme , biology , ecology
Several experimental approaches were used to determine whether rat liver and testes express an acyl‐CoA‐dependent δ8 desaturase. When [1‐ 14 C]5, 11, 14‐eicosatrienoic acid was injected via the tail vein, or directly into testes, it was incorporated into liver and testes phospholipids, but it was not metabolized to other labeled fatty acids. When [1‐ 14 C]11, 14‐eicosadienoic acid was injected, via the tail vein or directly into testes, or incubated with microsomes from both tissues, it was only metabolized to 5,11, 14‐eicosatrienoic acid. When ethyl 5,5,11,11,14,14‐d 6 ‐5,11,14‐eicosatrienoate was fed to rats maintained on a diet devoid of fat, it primarily replaced esteri‐fied 5,8,11‐eicosatrienoic acid, but not arachidonic acid. No labeled linoleate or arachidonate were detected. Dietary ethyl linoleate and ethyl 19,19,20,20‐d 4 ‐1,2‐ 13 C‐11,14‐eicosadienoate were about equally effective as precursors of esterified arachidonate. The doubly labeled 11,14‐eicosadienoate was metabolized primarily by conversion to 17,17,18,18‐d 4 ‐9,12‐ocatdeca‐dienoic acid, followed by its conversion to yield esterified arachidonate, with a mass four units greater than endogenous arachidonate. In addition, the doubly labeled substrate gave rise to a small amount of arachidonate, six mass units greater than endogenous arachidonate. No evidence was obtained, with the radiolabeled substrates, for the presence of a δ8 desaturase. However, the presence of an ion, six mass units greater than endogenous arachidonate when doubly labeled 11, 14‐eicosa‐dienoate was fed, suggests that a small amount of the substrate may have been metabolized by the sequential use of δ8 and δ5 desaturases.