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.
|Superclasses:||Biosynthesis → Fatty Acids and Lipids Biosynthesis → Fatty Acid Biosynthesis → Unusual 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. 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. The desaturated products of CPA-FAs, cyclopropene fatty acids (CPE-FAs), are only reported in plants. In plants, CPA-FAs are usually less abundant than CPE-FAs. CPA-FAs and CPE-FAs are distributed across several plant orders, most notably Malvales. CPE-FAs possibly function as anti-fungal agents of plants. 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 are desires in both reducing the CPE-FAs contents from feeding oilseeds and increasing the CPE-FAs contents in industrial oleochemical applications. EST profile of the Sterculia foetida cyclopropane synthase indicates a correlation of gene expression and high seed sterculic acid content.
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. In-vivo labeling experiments and in-vitro enzyme assay indicate that S-adenosylmethionine is the methylene donor for the synthesis of dihydrosterculic acid from oleic acid. The synthesized dihydrosterculic acid was only detected in phosphatidylcholine (predominantly on the sn-1 position), not in other phospholipids. Phosphatidylcholine is the direct substrate of cyclopropane synthase. Dihydrosterculic acid is further desaturated to sterculic acid by cyclopropane desaturase. Cyclopropane desaturase has not been characterized to date. It is interesting to note that even though dihydrosterculic acid is predominantly esterified at the sn-1 position, sterculic acid is equally distributed on sn-1 and sn-2 positions of phosphatidylcholine. It suggests that the dihydrosterculic acid synthesized at the sn-1 position may be removed from the sn-1 before further desaturation, and is subsequently re-incorporated 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
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