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 twomajor electrophoretic variants at the esterase-6 locus. The frequency ofthe EST 6F allozyme is greatest in populations in warmer latitudes, whereasthe EST 6S allozyme is predominant in colder latitudes. Latitudinal clinesin electromorph frequencies are found on three continents. Purifiedpreparations 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 ofthe EST 6 allozymes reveal that the two variants have differences in theirphysical and kinetic properties that may provide a basis for the selectivemaintenance of the polymorphisms and an explanation of the clinal variationobserved in natural populations.