Male Esterase 6 Catalyzes the Synthesis of a Sex Pheromone in Drosophila melanogaster Females.

Esterase 6, a component of the seminal fluid of Drosophila melanogaster males, hydrolyzes cis-vaccenyl acetate, a lipid made only by males, to cis-vaccenyl alcohol. This reaction occurs in the female reproductive tract and is virtually complete within 6 hours after copulation. Both the alcohol and the acetate decrease the number of matings among pairs of virgin flies in which the female is treated topically with these substances. Although females tested 10 minutes after copulation elicit less courtship than virgin females, females tested 6 hours after copulation stimulate even less courtship if they received active esterase 6 in the seminal fluid of their respective mates. Either the alcohol or a derivative appears to be an antiaphrodisiac that decreases courtship elicited by inseminated females and thus reduces the probability of further mating. Thus the activity of the pheromone depends on a final reaction which occurs in the female, using both substrate and enzyme provided by the male.

Studies of esterase 6 in Drosophila melanogaster. XVIII. Biochemical differences between the slow and fast allozymes.

Most natural populations of Drosophila melanogaster are polymorphic for two major electrophoretic variants at the esterase-6 locus. The frequency of the EST 6F allozyme is greatest in populations in warmer latitudes, whereas the EST 6S allozyme is predominant in colder latitudes. Latitudinal clines in electromorph frequencies are found on three continents. Purified preparations of the allozymes have been characterized for their pH optimum, substrate specificity, organophosphate inhibition, alcohol activation, thermal stability, and kinetic parameters. These and previous analyses of the EST 6 allozymes reveal that the two variants have differences in their physical and kinetic properties that may provide a basis for the selective maintenance of the polymorphisms and an explanation of the clinal variation observed in natural populations.

Studies of esterase 6 in Drosophila melanogaster. XIII. Purification and characterization of the two major isozymes.

Esterase-6 (EST 6; carboxylic-ester hydrolase; EC 3.1.1.1) from Drosophila melanogaster was purified to homogenity. Purified enzyme occurs as two closely moving isozymes, slow (EST 6S) and fast (EST 6F), on native polyacrylamide gel electrophoresis. Except for slight differences in their mobility, the two isozymes share similar molecular and catalytic properties. Both isozymes are glycoproteins and have an apparent molecular weight of 62,000 to 65,000 as judged by analytical gel filtration and sodium dodecyl sulfate (SDS) electrophoresis. They have identical mobility on SDS-polyacrylamide gels and an isoelectric point of 4.5. Each isozyme has a single active catalytic site as confirmed by titration with 0,0-diethyl-p-nitrophenyl phosphate (Paraoxon). We conclude that EST 6 is a monomeric enzyme. The amino acid composition of the two isozymes is very similar and both variants lack half-cystine residues. The low pI of the enzyme is due in part to a relatively high proportion of glutamic and aspartic amino acid residues. Characterization of the kinetic parameters of the isozymes using beta-naphthyl and p-nitrophenyl esters revealed no statistically significant differences in catalytic efficiency. There is, however, a suggestion that the two isozymes may differ in their substrate specificity.