title: Arachidonic acid synthetic pathways of the oyster protozoan parasite, Perkinsus marinus: evidence for usage of a delta-8 pathway.
abstract: The meront stage of the oyster protozoan parasite, Perkinsus marinus, is capable of synthesizing saturated and unsaturated fatty acids including the essential fatty acid, arachidonic acid [20:4(n-6)]. Eukaryotes employ either delta-6 (Delta-6) or delta-8 (Delta-8) desaturase pathway or both to synthesize arachidonic acid. To elucidate the arachidonic acid synthetic pathways in P. marinus, meronts were incubated with deuterium-labeled precursors [18:1(n-9)-d6, 18:2(n-6)-d4, 18:3(n-3)-d4, and 20:3(n-3)-d8]. The lipids were extracted, converted to fatty acid methyl esters, and analyzed using gas chromatography/mass spectrometry and gas chromatography/flame ionization detection. Deuterium-labeled 18:2(n-6), 20:2(n-6), 20:3(n-6), and 20:4(n-6) were detected in meront lipids after 1-, 3-, 5-, and 10-day incubation with 18:1(n-9)-d6. Deuterium-labeled 20:2(n-6), 20:3(n-6) and 20:4(n-6) were found in lipids from meronts after incubation with 18:2(n-6)-d4 methyl ester. No labeled 18:3(n-6) was detected in either incubation. Apparently, when incubated with 18:1(n-9)-d6, the parasite first desaturated 18:1(n-9)-d6 to 18:2(n-6)-d6 by Delta-12 desaturase, then to 20:2(n-6)-d6 by elongation, and ultimately desaturated to 20:3(n-6)-d6 and 20:4(n-6)-d6 using the sequential Delta-8 and Delta-5 desaturation. Similarly, when incubated with 18:2(n-6)-d4, P. marinus converted the 18:2(n-6)-d4 to 20:2(n-6)-d4 by elongation and 20:2(n-6)-d4 to 20:3(n-6)-d4 by Delta-8 desaturase then by Delta-5 desaturase to 20:4(n-6)-d4. These results provide evidence that P. marinus employed the Delta-8 rather Delta-6 pathway for arachidonic acid synthesis. Additional support for the presence of a Delta-8 pathway was the demonstrated ability of the parasite to metabolize 18:3(n-3)-d4 to 20:3(n-3)-d4 and 20:4(n-3)-d4, and 20:3(n-3)-d8 to 20:4(n-3)-d6 and 20:5(n-3)-d6 using the sequential position-specific Delta-8 and Delta-5 desaturases.
authors.affiliation: Virginia Institute of Marine Science, School of Marine Science, Gloucester Point, VA 23062, USA. chu@vims.edu
authors.forename: Fu-Lin E
authors.initials: FL
authors.lastname: Chu
authors.forename: Eric D
authors.initials: ED
authors.lastname: Lund
authors.forename: Ellen
authors.initials: E
authors.lastname: Harvey
authors.forename: Richard
authors.initials: R
authors.lastname: Adlof
mesh_terms: D000818:Animals; D016718:Arachidonic Acid / Q000096:biosynthesis* / Q000737:chemistry; D002849:Chromatography, Gas; D000090943:Delta-5 Fatty Acid Desaturase; D056890:Eukaryota / Q000378:metabolism*; D044943:Fatty Acid Desaturases / Q000378:metabolism*; D005227:Fatty Acids / Q000378:metabolism*; D005228:Fatty Acids, Essential / Q000096:biosynthesis; D010125:Ostreidae / Q000469:parasitology*
chemical_list: D000090943:Delta-5 Fatty Acid Desaturase; D005227:Fatty Acids; D005228:Fatty Acids, Essential; D016718:Arachidonic Acid; D044943:Fatty Acid Desaturases; C119257:delta-8 fatty acid desaturase