Substrate specificity of the epoxidation reaction in sex pheromone biosynthesis of the Japanese giant looper (Lepidoptera: Geometridae)

Abstract

Female moths of the Japanese giant looper ( Ascotis selenaria cretacea, Lepidoptera: Geometridae) secrete ( Z, Z)-6,9- cis-3,4-epoxynonadecadiene as a sex pheromone component. To the pheromone glands of the decapitated females, [19,19,19-D 3]( Z, Z, Z)-3,6,9-nonadecatriene was applied after an injection of pheromone biosynthesis activating neuropeptide. GC-MS analysis of the gland extract showed its specific conversion into the pheromonal cis-3,4-epoxide indicating that the C 19 triene which had been identified in the gland was a precursor of the pheromone. In order to examine the substrate specificity of the enzyme catalyzing this epoxidation step, several unsaturated hydrocarbons not occurring in the gland were applied to it. Not only ( Z, Z, Z)-3,6,9-trienes with varying chain lengths (C 17, C 18 and C 20 to C 22) but ( Z, Z)-3,6-dienes (C 17, C 19 and C 20) were converted into the corresponding cis-3,4-epoxides in a rather good yield, while no 6,7- and 9,10-epoxides could be detected. ( Z)-3-Nonadecene was also changed to the cis-epoxide, but ( E)-3-, ( Z)-2- and ( Z)-4-double bonds in the C 19 chain were not oxidized. These in vivo experiments revealed that the monooxygenase regiospecifically attacked the ( Z)-3-double bond of straight chain hydrocarbons regardless of their length and degree of unsaturation.