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Biosynthesis of arachidonic acid in the oleaginous microalga Parietochloris incisa (Chlorophyceae): Radiolabeling studies
Author(s) -
Bigogno Chiara,
KhozinGoldberg Inna,
Adlerstein Daniel,
Cohen Zvi
Publication year - 2002
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/s11745-002-0882-6
Subject(s) - biochemistry , galactolipids , biosynthesis , arachidonic acid , biology , chlorophyceae , polyunsaturated fatty acid , oleic acid , algae , linoleic acid , linolenic acid , fatty acid , chlorophyta , chloroplast , botany , enzyme , gene
The fresh‐water green alga Parietochloris incisa is the richest plant source of the PUFA arachidonic acid (20∶4n−6, AA). To elucidate the biosynthesis of AA in this alga we labeled cultures of P. incisa with radioactive precursors. Pulse chase labeling with acetate resulted in its incorporation via the de novo biosynthesis pathway of FA. However, labeled acetate was also utilized for the elongation of C 16 and C 18 PUFA. Labeling with [1‐ 14 C]oleic acid has shown that the first steps of the lipid‐linked FA desaturations utilize cytoplasmic lipids. PC and diacylglyceryltrimethylhomoserine are the major lipids involved as acyl carriers for the Δ12 and Δ6 desaturations of oleic acid, leading sequentially to linoleic and γ‐linolenic acids. The latter is released from its lipid carrier and elongated to 20∶3n−6, which is reincorporated primarily into PF and PC and finally desaturated to AA. Galactolipids, mostly monogalctosyldiacylglycerol (MGDG), serve as substrates for the chloroplastic Δ12 desaturase and, apparently, the ω3 desaturation, common to higher plants and many green algae. The predominant sequence desaturates the 18∶1/16∶0 molecular species of MGDG stepwise to the 18∶3n−3/16∶3n−3 molecular species similar to the prokaryotic pathway of higher plants and green algae.