β-D-phosphogalactoside galactohydrolase of Streptococcus faecalis and the inhibition of its synthesis by glucose

Abstract

The lactose hydrolysing system of Streptococcus faecalis is described. It is closely related to that one of the group N streptococci as it consists of a β-D-phosphogalactoside galactohydrolase β-Pgal). The uptake of methyl-β-D-thiogalactoside (TMG), lactose, and glucose is maintained by the phosphoenolpyruvate-dependent phosphotransferase system (PTS) but the uptake of galactose is not. The induction time is 6–7 min. Inducers are lactose and galactose but not isopropyl-β-D-galactoside (IPTG) and TMG. In the presence of glucose, mannose, and maltose no induction of β-Pgal occurs but pyruvate and glycerol allow induction. The competitive inhibition of uptake of TMG by glucose suggests inducer exclusion by this sugar. TMG accumulates in the cells exclusively as a derivative.