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Updated: Aug 10, 2026
09:58
Light-driven Enzymatic Decarboxylation
Published on: May 22, 2016
Endoplasmic oleoyl-PC desaturase references the second double bond
J L Schwartzbeck1, S Jung, A G Abbott
1Department of Biological Sciences, Clemson University, Clemson, SC 29634-0326, USA.
Phytochemistry
|June 9, 2001
Summary
The fad2 gene product, a plant oleoyl-PC desaturase, identifies substrate double bond locations by referencing existing double bonds, not just ends. This mechanism, Delta(x+3), precisely positions new double bonds in fatty acids.
Area of Science:
- Biochemistry
- Plant Molecular Biology
- Enzymology
Background:
- The fad2 gene encodes the microsomal oleoyl-PC desaturase in higher plants.
- Previous understanding of plant desaturase regiospecificity was limited, focusing on carboxyl or methyl termini.
- Microsomal desaturases are crucial for introducing unsaturation into fatty acids within membrane lipids.
Purpose of the Study:
- To elucidate the precise regiospecificity of the plant oleoyl-PC desaturase (fad2 gene product).
- To determine the mechanism by which this enzyme locates and introduces a second double bond into monounsaturated fatty acid substrates.
- To validate the findings using a heterologous expression system.
Main Methods:
- Cloning and expression of peanut (Arachis hypogaea L) oleoyl-PC desaturase cDNA in yeast (Saccharomyces cerevisiae).
- Analysis of fatty acid desaturation products in yeast membrane lipids.
- Characterization of substrate specificity using endogenous and supplemented fatty acids.
Main Results:
- The expressed enzyme desaturated endogenous palmitoleate to 9(Z)12(Z)C16:2 and oleate to linoleate (9(Z)12(Z) octadecadienoate).
- Exogenously supplied cis 10-nonadecenoate was desaturated to 10(Z)13(Z)C19:2.
- The regiospecificity was best described by the Delta(x+3) rule, where x indicates the position of the existing double bond.
Conclusions:
- The plant oleoyl-PC desaturase (fad2) exhibits unique regiospecificity, referencing the existing double bond rather than the fatty acid termini.
- The Delta(x+3) rule accurately predicts the enzyme's activity on monounsaturated fatty acyl substrates.
- This finding refines our understanding of fatty acid metabolism and desaturation in plants.
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