Inhibition by 6-O-tosyl galactosides of beta-galactoside phosphorylation and transport by the lactose phosphotransferase system of Staphylococcus aureus.

The effect of various galactose derivatives, substituted at C-6, on the phosphoenolpyruvate:beta-galactoside phosphotransferase system of Staphylococcus aureus was studied. Cells were grown by an improved procedure, which resulted in a 5- to 10-fold increase in cell yield. The four protein components of the system were separated. A membrane fraction containing negligible levels of the soluble components was prepared by alternate cycles of sonic treatment and differential centrifugation. The in vitro system reconstituted from these fractions was used to test the ability of the galactose derivatives to inhibit the phosphorylation of lactose analogs, under conditions where the membrane-bound component, Enzyme IIlac, was rate limiting. Derivaites in which the hydroxyl group of C-6 was missing, or replaced by a fluoro, O-methyl, or carboxyl group had no affinity for Enzyme IIlac, as judged by their inability to inhibit phosphorylation. Surprisingly, derivatives containing arylsulfonyl groups at C-6 were potent inhibitors; the O-tosyl compound has an apparent affinity five times that of galactose. The arylsulfonyl substitution in an absolute requirement; neither O-benzyl or O-methanesulfonyl derivatives were inhibitory. The specificity of the inhibition by tosyl derivatives parallels that of unsubstituted substrates; tosyl galactosides of the beta configuration were inhibitory, but those of the alpha configuration were not. The tosyl derivatives also strongly inhibited the uptake of lactose analogs into whole cells; the requirement for the arylsulfonyl moiety was again observed. The chemical analogy between the tosyl galactosides and possible intermediates in the transport-phosphorylation step catalyzed by Enzyme IIlac provides a possible explanation for the unexpected properties of these derivatives.