beta-Galactosidase is induced by hormone in Drosophila melanogaster cell cultures

Drosophila melanogaster cell lines Kc and Ca and clones FC and RF6, cultured in vitro, have no detectable beta-galactosidase (beta-galactoside galactohydrolase, EC 3.2.1.23) activity (as measured by hydrolysis of o-nitrophenyl-beta-D-galoctoside). Ecdysterone, a hormonal steroid of critical importance in insect physiology, clearly induces beta-galactosidase activity in D. melanogaster cells cultured in vitro. Induction occurs in cell lines or clones known to be sensitive to ecdysterone (K, Ca, and Fc) and does not occur in clones known to be resistant to the hormone (RF6). Some properties of the hormone-induced beta-galactosidase activity were studied. The Km for o-nitrophenyl galactoside is 0.35 mM and the Ki for lactose is 12 mM (similar to those of Escherichia coli beta-galactosidase); the activity can be recovered after sodium dodecyl sulfate treatment; the enzyme is a tetramer (Mr of the monomer is 64,000).