Influence of Introduction of a Fructosyl Group into Galactosylglucoses on their β-Galactosidase-inducing Activity

Abstract

INTRODUCTION of a fructose group at the reducing carbon position of melibiose (to form raffinose) is known to abolish the β-galactosidase-inducing capacity of this α-galactoside in Escherichia coli ^1,2. The question arises whether this effect of the fructose group applies also to induction effected by β-galactosides. A study was therefore made of the β-galactosidase-inducing capacity of an homologous β-galactosidic oligosaccharide pair, namely, the pair lactose and α-lactosyl-β-fructofuranoside³. This last sugar, which will be referred to as ‘lactsucrose’, has a terminal β-galactosidic linkage, and is readily cleaved to galactose and sucrose both by E. coli K–12 β-galactosidase in solution and by a washed suspension of lactose-induced cells of this strain (Table 1). It proved, however, to be a negligible inducer of the (β-galactosidase. Thus, the relative behaviour of lactose and lactsucrose resembles that of melibiose and raffinose in respect of the capacity to induce β-galactosidase in E. coli K–12. Moreover, it has also been shown recently that raffinose can be metabolized by melibiose-induced cells⁶. This indicates that raffinose is able to penetrate such cells. The cleavage of lactsucrose by lactose-induced cells indicates similarly that lactsucrose can enter these cells.