title: Methyl-directed desaturation of arachidonic to eicosapentaenoic acid in the fungus, Saprolegnia parasitica.
abstract: The lipids of Saprolegnia parasitica contain 5,8,11,14,17-eicosapentaenoic acid as major constituent. No other acid having (n-3) structure was detected, but 5,8,11,14-eicosatetraenoic (arachidonic) acid and its common precursors of (n-6) structure are present in significant amounts. During rapid growth of the organism, [1-14C]acetate was efficiently incorporated into fatty acids. Arachidonic acid was labeled after 2 h to nearly the same extent as any precursor acid and 14C in eicosapentaenoic acid reached this level within 6 h. Results of incubations with labeled fatty acids indicated that, in S. parasitica, oleic, linoleic, (6,9,12)-linolenic and arachidonic acids are major intermediates in the pathway to eicosapentaenoic acid. Methyl-directed desaturation of (n-6) to (n-3) acids does not occur with C18 acids but is specific for the polyunsaturated C20 chain length. Arachidonic acid is the direct precursor of eicosapentaenoic acid.
mesh_terms: D000085:Acetates / Q000378:metabolism; D001095:Arachidonic Acids / Q000378:metabolism*; D004537:Eicosanoic Acids / Q000096:biosynthesis*; D005231:Fatty Acids, Unsaturated / Q000096:biosynthesis*; D005658:Fungi / Q000378:metabolism*; D009868:Oomycetes / Q000378:metabolism*
chemical_list: D000085:Acetates; D001095:Arachidonic Acids; D004537:Eicosanoic Acids; D005231:Fatty Acids, Unsaturated