Mechanism of regulation of the lactose permease by the phosphotransferase system in Escherichia coli: evidence for protein-protein interaction.

Binding of enzyme IIIglc to membranes was demonstrated in vitro, using membrane fragments from an E. coli strain which produces elevated levels of the lactose permease. Lactose and other substrates of the lactose permease enhanced the binding, but phosphoenolpyruvate decreased it in the presence of enzyme I and HPr. HPr also bound to the membranes under some conditions. The results support a model of permease regulation involving allosteric protein-protein interactions.