Bioorganic chemistry of plant lipid desaturation

Abstract

The desaturation of long-chain fatty acids is a ubiquitous biotransformation which plays a critical role in the biosynthesis of plant lipids. Species-specific variations lead to unusual fatty acid signatures. Of particular interest is the unique ability of desaturases to oxidize unactivated hydrocarbon chains in such a chemo-, regio- and stereoselective manner. As part of ongoing research into the structure/activity relationships of this large class of enzymes, useful mechanistic tools have been developed to probe the active site. Recently a combination of stereo- and regiospecific deuterium, sulfur and fluorine labelling has been used to study the mechanism of a soluble plant Δ9 desaturase. The study of several membrane-bound desaturases has led to the conclusion that the dehydrogenation (desaturation) process is initiated by a kinetically important hydrogen activation step at the carbon of the incipient double bond which is closest to the acyl terminus of the fatty acid chain. A detailed analysis of a related 1,4-desaturation process has also been carried out.