The same rat Delta6-desaturase not only acts on 18- but also on 24-carbon fatty acids in very-long-chain polyunsaturated fatty acid biosynthesis.
The recently cloned Delta6-desaturase is known to catalyse the first step in very-long-chain polyunsaturated fatty acid biosynthesis, i.e. the desaturation of linoleic and alpha-linolenic acids. The hypothesis that this enzyme could also catalyse the terminal desaturation step, i.e. the desaturation of 24-carbon highly unsaturated fatty acids, has never been elucidated. To test this hypothesis, the activity of rat Delta6-desaturase expressed in COS-7 cells was investigated. Recombinant Delta6-desaturase expression was analysed by Western blot, revealing a single band at 45 kDa. The putative involvement of this enzyme in the Delta6-desaturation of C(24:5) n-3 to C(24:6) n-3 was measured by incubating transfected cells with C(22:5) n-3. Whereas both transfected and non-transfected COS-7 cells were able to synthesize C(24:5) n-3 by elongation of C(22:5) n-3, only cells expressing Delta6-desaturase were also able to produce C(24:6) n-3. In addition, Delta6-desaturation of [1-(14)C]C(24:5) n-3 was assayed in vitro in homogenates from COS-7 cells expressing Delta6-desaturase or not, showing that Delta6-desaturase catalyses the conversion of C(24:5) n-3 to C(24:6) n-3. Evidence is therefore presented that the same rat Delta6-desaturase catalyses not only the conversion of C(18:3) n-3 to C(18:4) n-3, but also the conversion of C(24:5) n-3 to C(24:6) n-3. A similar mechanism in the n-6 series is strongly suggested.
D'andrea
Sabine
S
Laboratoire de Biochimie, INRA-ENSA, 65 rue de Saint-Brieuc, CS84215, 35042 Rennes cedex, France.
Guillou
Hervé
H
Jan
Sophie
S
Catheline
Daniel
D
Thibault
Jean-Noël
JN
Bouriel
Monique
M
Rioux
Vincent
V
Legrand
Philippe
P
D000818:Animals; D015153:Blotting, Western; D019556:COS Cells; D002384:Catalysis; D002849:Chromatography, Gas; D018076:DNA, Complementary / Q000378:metabolism; D044943:Fatty Acid Desaturases / Q000378:metabolism*; D005227:Fatty Acids / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000096:biosynthesis*; D050602:Linoleoyl-CoA Desaturase; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D013997:Time Factors; D014162:Transfection
D018076:DNA, Complementary; D005227:Fatty Acids; D005231:Fatty Acids, Unsaturated; D011994:Recombinant Proteins; D044943:Fatty Acid Desaturases; D050602:Linoleoyl-CoA Desaturase