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Hidden stereospecificity in the biosynthesis of divinyl ether fatty acids

2005; Wiley; Volume: 272; Issue: 3 Linguagem: Inglês

10.1111/j.1742-4658.2004.04510.x

1742-4658

Mats Hámberg,

Nitrogen and Sulfur Effects on Brassica

Incubations of [8( R )‐ 2 H]9( S )‐hydroperoxy‐10( E ),12( Z )‐octadecadienoic acid, [14( R )‐ 2 H]13( S )‐hydroperoxy‐9( Z ),11( E )‐octadecadienoic acid and [14( S )‐ 2 H]13( S )‐hydroperoxy‐9( Z ),11( E )‐octadecadienoic acid were performed with preparations of plant tissues containing divinyl ether synthases. In agreement with previous studies, generation of colneleic acid from the 8( R )‐deuterated 9( S )‐hydroperoxide was accompanied by loss of most of the deuterium label (retention, 8%), however, the opposite result (98% retention) was observed in the generation of 8( Z )‐colneleic acid from the same hydroperoxide. Formation of etheroleic acid and 11( Z )‐etheroleic acid from the 14( R )‐deuterated 13( S )‐hydroperoxide was accompanied by loss of most of the deuterium (retention, 7–8%), and, as expected, biosynthesis of these divinyl ethers from the corresponding 14( S )‐deuterated hydroperoxide was accompanied by retention of deuterium (retention, 94–98%). Biosynthesis of ω5( Z )‐etheroleic acid from the 14( R )‐ and 14( S )‐deuterated 13( S )‐hydroperoxides showed the opposite results, i.e. 98% retention and 4% retention, respectively. The experiments demonstrated that biosynthesis of divinyl ether fatty acids from linoleic acid 9‐ and 13‐hydroperoxides takes place by a mechanism that involves stereospecific abstraction of one of the two hydrogen atoms α to the hydroperoxide carbon. Furthermore, a consistent relationship between the absolute configuration of the hydrogen atom eliminated ( R or S ) and the configuration of the introduced vinyl ether double bond ( E or Z ) emerged from these results. Thus, irrespective of which hydroperoxide regioisomer served as the substrate, divinyl ether synthases abstracting the pro‐R hydrogen generated divinyl ethers having an E vinyl ether double bond, whereas enzymes abstracting the pro‐S hydrogen produced divinyl ethers having a Z vinyl ether double bond.