THE OCCURRENCE OF β-GALACTOSIDASE IN ESCHERICHIA COLI

Abstract

The "adaptive" enzyme beta-D-galactosidase (lactase) was found in E. coli, strain K-12, regardless of the C source used for growth. The enzyme in cell extracts was measured by the use of a chromogenic substrate, o-nitrophenyl-beta-D-galactoside. The level of beta-D-galactosidase activity varied with the C source; marked stimulation of enzyme production was afforded by galactose and melibiose, as well as lactose. Melibiose, although not a substrate for beta-galactosidase was more effective in stimulating enzyme production than was the beta-galactoside lactose. The beta-galactosidases produced by cells grown on various C sources are serologically identical. Lyxose and raffinose, which do not serve as C sources, also stimulate beta-galactosidase formation under the proper conditions. The beta-galactosidase-inhibiting capacities of various sugars and their abil-ity to stimulate enzyme formation are unrelated. The results ob-tained support the conclusion that adaptive enzyme formation is not a de novo process induced by the presence of specific substrate.