This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Synonyms: cyclopropane and cyclopropene fatty acid biosynthesis
|Superclasses:||Biosynthesis → Fatty Acid and Lipid Biosynthesis → Fatty Acid Biosynthesis → Cyclopropane Fatty Acids Biosynthesis|
Some taxa known to possess this pathway include : Sterculia foetida
Expected Taxonomic Range: Embryophyta
Cyclopropane fatty acids (CPA-FAs), unusual fatty acids containing three-carbon cyclic rings, are found in both bacteria and plants [Grogan97]. One striking difference between the bacteria CPA-FAs and the plant CPA-FAs is that the bacteria CPA-FAs are normally esterified at the sn-2 position of phosphatidylethanolamine, whereas the plant CPA-FAs are preferentially esterified at the sn-1 position of phosphatidylcholine. In plants most CPA-FAs are desaturated to cyclopropene fatty acids (CPE-FAs). CPA-FAs and CPE-FAs are distributed across several plant orders, including certain gymnosperms, Malvales, and Sapindales [Yu11].
Plant CPE-FAs may function as anti-fungal agents. Feeding animals with CPE-FA-containing oilseeds, such as cotton seed meal, causes physiological disorders due to the fact that CPE-FAs are strong inhibitors of fatty acid desaturases in animals. There is an interest in both reducing the CPE-FAs contents in feeding oilseeds and increasing the CPE-FAs contents for industrial oleochemical applications.
About This Pathway
Our knowledge of the plant pathway of cyclopropane and cyclopropene biosynthesis mainly came from studies of Sterculia foetida, a tropical tree whose seed oil contains 65-78% CPE-FAs, mainly sterculic acids.
The key enzyme in the pathway is cyclopropane synthase, an enzyme that converts the double bond of oleate to a cyclopropane group. The enzyme does not act of free acids, but on oleate groups incorporated into phosphatidylcholine. In vivo labeling experiments and in vitro enzyme assays indicate that S-adenosylmethionine is the methylene donor for the synthesis of dihydrosterculate from oleate. The synthesized dihydrosterculate was only detected in phosphatidylcholine (predominantly on the sn-1 position), not in other phospholipids. EST profile of the Sterculia foetida cyclopropane synthase indicates a correlation of gene expression and high seed stercuate content.
Dihydrosterculate is further desaturated to sterculate by the enzyme cyclopropane desaturase, which has not been characterized to date. It is interesting to note that even though dihydrosterculate is predominantly esterified at the sn-1 position, sterculate is equally distributed on sn-1 and sn-2 positions of phosphatidylcholine, suggesting that the dihydrosterculate synthesized at the sn-1 position may be removed from the lipid before further desaturation, followed by reincorporation into the sn-2 position.
Bao02: Bao X, Katz S, Pollard M, Ohlrogge J (2002). "Carbocyclic fatty acids in plants: biochemical and molecular genetic characterization of cyclopropane fatty acid synthesis of Sterculiafoetida." Proc Natl Acad Sci U S A 99(10);7172-7. PMID: 11997456
Yu11: Yu XH, Rawat R, Shanklin J (2011). "Characterization and analysis of the cotton cyclopropane fatty acid synthase family and their contribution to cyclopropane fatty acid synthesis." BMC Plant Biol 11;97. PMID: 21612656
Goldfine71: Goldfine H, Panos C (1971). "Phospholipids of Clostridium butyricum. IV. Analysis of the positional isomers of monounsaturated and cyclopropane fatty acids and alk-1'-enyl ethers by capillary column chromatography." J Lipid Res 12(2);214-20. PMID: 5554109
Jaworski74: Jaworski JG, Stumpf PK (1974). "Fat metabolism in higher plants. Properties of a soluble stearyl-acyl carrier protein desaturase from maturing Carthamus tinctorius." Arch Biochem Biophys 162(1);158-65. PMID: 4831331
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