Biochemical properties, homology, and genetic variation of Drosophila “nonspecific” esterases

The biochemical properties and tissue distribution of two major, soluble “nonspecific” esterases have been studied in Drosophila melanogaster, D. pseudoobscura, and related species. The “α-like” activity is due to a monomer enzyme (MW⋍60 kd) having a nonspecific tissue distribution, which was inhibited by p-hydroxymercuribenzoate (5×10−4m) plus eserine (1×10−5m) and was relatively unstable during polyacrylamide gel electrophoresis. Electrophoretograms of this enzyme could be enhanced by treating gels with β-mercaptoethanol before staining. This procedure allowed the identification of a new α-esterase (Est-4) in D. pseudoobscura. The “β-like” esterase activity (EC 3.1.1.1) is due to a dimer (MW⋍120 kd) in most Drosophila species. D. melanogaster and its siblings (D. simulans and D. mauritiana) were exceptions in which this enzyme had an unusual tissue distribution (increased activity in the male reproductive system) and was a monomer (MW⋍60 kd). Differences in the genetic variability of these esterases are discussed and interpreted by a population expansion model rather than by differences in biochemical properties of enzyme forms.