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Cryptoregiochemistry of the Δ11-Myristoyl-CoA Desaturase Involved in the Biosynthesis of Spodoptera littoralis Sex Pheromone†
journal contribution
posted on 1999-10-29, 00:00 authored by Anna Pinilla, Francisco Camps, Gemma FabriasMany moth species biosynthesize their sex pheromones by the action of unique desaturases.
These membrane-bound family of enzymes are especially interesting, since some of them produce (E)-unsaturated fatty acids either exclusively or along with the (Z)-isomer. In this article we present the first
mechanistic study on one of these enzymes, namely, the Δ11-myristoyl-CoA desaturase of the moth
Spodoptera littoralis. Intermolecular primary isotope effect determinations were performed in competition
experiments. The unusual use of odd-number fatty acids, tridecanoic acid and deuterium-labeled tridecanoic
acid, in these experiments showed the existence of a large isotope effect for the carbon−hydrogen bond
cleavage at C11, but no isotope discrimination occurred in the removal of C12−H. The results of the
competitive experiments are consistent with the hypothesis that this Δ11-desaturase involves a first slow,
isotope-sensitive C11−H bond cleavage, with probable formation of an unstable intermediate, followed
by a second fast C12−H bond removal. We suggest that a single enzyme may be responsible for the
formation of both (Z)- and (E)-11-tetradecenoic acids by accommodating both gauche and anti conformers
of the substrate, respectively. It is also possible that two mechanistically identical discrete enzymes are
involved in each desaturation. In this case, the geometry of the resulting double bond would result from
the different conformation adopted by the acyl substrate at each enzyme active site.