scholarly journals Comparative Analysis of Fatty Acid Desaturases in Cyanobacterial Genomes

2008 ◽  
Vol 2008 ◽  
pp. 1-25 ◽  
Author(s):  
Xiaoyuan Chi ◽  
Qingli Yang ◽  
Fangqing Zhao ◽  
Song Qin ◽  
Yu Yang ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Unsaturated Fatty Acids ◽  
Fatty Acid Desaturases ◽  
Highly Unsaturated Fatty Acids ◽  
Acyl Lipid ◽  
Cyanobacterial Species ◽  
Hydrocarbon Chains ◽  
Lipid Desaturation ◽  
Calcareous Rock

Fatty acid desaturases are enzymes that introduce double bonds into the hydrocarbon chains of fatty acids. The fatty acid desaturases from 37 cyanobacterial genomes were identified and classified based upon their conserved histidine-rich motifs and phylogenetic analysis, which help to determine the amounts and distributions of desaturases in cyanobacterial species. The filamentous orN2-fixing cyanobacteria usually possess more types of fatty acid desaturases than that of unicellular species. The pathway of acyl-lipid desaturation for unicellular marine cyanobacteriaSynechococcusandProchlorococcusdiffers from that of other cyanobacteria, indicating different phylogenetic histories of the two genera from other cyanobacteria isolated from freshwater, soil, or symbiont. StrainGloeobacter violaceusPCC 7421 was isolated from calcareous rock and lacks thylakoid membranes. The types and amounts of desaturases of this strain are distinct to those of other cyanobacteria, reflecting the earliest divergence of it from the cyanobacterial line. Three thermophilic unicellular strains,Thermosynechococcus elongatusBP-1 and twoSynechococcusYellowstone species, lack highly unsaturated fatty acids in lipids and contain only oneΔ9desaturase in contrast with mesophilic strains, which is probably due to their thermic habitats. Thus, the amounts and types of fatty acid desaturases are various among different cyanobacterial species, which may result from the adaption to environments in evolution.

scholarly journals The same rat Δ6-desaturase not only acts on 18- but also on 24-carbon fatty acids in very-long-chain polyunsaturated fatty acid biosynthesis

2002 ◽  
Vol 364 (1) ◽  
pp. 49-55 ◽  
Author(s):  
Sabine D'ANDREA ◽  
Hervé GUILLOU ◽  
Sophie JAN ◽  
Daniel CATHELINE ◽  
Jean-Noël THIBAULT ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Polyunsaturated Fatty Acid ◽  
Unsaturated Fatty Acids ◽  
Fatty Acid Biosynthesis ◽  
Chain Polyunsaturated Fatty Acid ◽  
Acid Biosynthesis ◽  
Highly Unsaturated Fatty Acids ◽  
Long Chain ◽  
Δ6 Desaturase

The recently cloned Δ6-desaturase is known to catalyse the first step in very-long-chain polyunsaturated fatty acid biosynthesis, i.e. the desaturation of linoleic and α-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 Δ6-desaturase expressed in COS-7 cells was investigated. Recombinant Δ6-desaturase expression was analysed by Western blot, revealing a single band at 45kDa. The putative involvement of this enzyme in the Δ6-desaturation of C24:5n-3 to C24:6n-3 was measured by incubating transfected cells with C22:5n-3. Whereas both transfected and non-transfected COS-7 cells were able to synthesize C24:5n-3 by elongation of C22:5n-3, only cells expressing Δ6-desaturase were also able to produce C24:6n-3. In addition, Δ6-desaturation of [1-14C]C24:5n-3 was assayed invitro in homogenates from COS-7 cells expressing Δ6-desaturase or not, showing that Δ6-desaturase catalyses the conversion of C24:5n-3 to C24:6n-3. Evidence is therefore presented that the same rat Δ6-desaturase catalyses not only the conversion of C18:3n-3 to C18:4n-3, but also the conversion of C24:5n-3 to C24:6n-3. A similar mechanism in the n-6 series is strongly suggested.

Substrate specificity, regioselectivity and cryptoregiochemistry of plant and animal ω-3 fatty acid desaturases

2000 ◽  
Vol 28 (6) ◽  
pp. 632-635 ◽  
Author(s):  
D. Meesapyodsuk ◽  
D. W. Reed ◽  
C. K. Savile ◽  
P. H. Buist ◽  
U. A. Schäfer ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Unsaturated Fatty Acids ◽  
Bond Cleavage ◽  
Isotope Effects ◽  
Fatty Acid Desaturases ◽  
Yeast Saccharomyces Cerevisiae ◽  
Kinetic Isotope ◽  
Acid Analogue ◽  
And Function

In order to define the substrate requirements, regiochemistry and cryptoregiochemistry of the ω-3 fatty acid desaturases involved in polyunsaturated fatty acid formation, the genes Fad3 and fat-1 from Brassica napus and the nematode Caenorhabditis elegans respectively were expressed in baker's yeast (Saccharomyces cerevisiae). Various fatty acids, including deuterium-labelled thia-fatty acids, were supplied to growing cultures of transformed yeast. The results from GC-MS analysis of the desaturated products indicate that both the plant and animal desaturases act on unsaturated substrates of 16–20 carbons with a preference for ω-6-unsaturated fatty acids. The regioselectivities of both enzymes were confirmed to be that of ω-3 desaturases. The primary deuterium kinetic isotope effects at C-15 and C-16 of a C18 fatty acid analogue were measured via competitive incubation experiments. Whereas kH/kD at the ω-3 position was shown to be large, essentially no kinetic isotope effect at the ω-2 position was observed for the plant or the nematode enzymes. These results indicate that ω-3 desaturation is initiated by an energetically difficult C-H bond cleavage at the carbon closer to the carboxyl terminus. These results will be discussed in the context of a general model relating the structure and function of membrane-bound fatty acid desaturases featuring different regioselectivities.

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