Regulation of Lactose Transport by the Phosphoenolpyruvate‐Sugar Phosphotransferase System in Membrane Vesicles of Escherichia coli

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Abstract
Regulation of lactose uptake by the phosphoenolpyruvate-sugar phosphotransferase system (PTS) has been demonstrated in membrane vesicles of Escherichia coli strain ML308-225. Substrates of the phosphotransferase system inhibited D-lactate energized uptake of lactose but did not inhibit uptake of either L-alanine or L-proline. This inhibition was reversed by intravesicular (but not extravesicular) phosphoenolpyruvate. Lactose uptake was also inhibited by enzyme IIIglc preparations that were shocked into the vesicles, and this inhibition was reversed by phosphoenolpyruvate. Intravesicular HPr and enzyme I stimulated methyl α-glucoside uptake but did not inhibit or stimulate lactose accumulation. Vesicles maintained at 0°C for several days partially lost 1) the ability to take up lactose, 2) the ability to accumulate PTS substrates, and 3) PTS-mediated regulation. Phosphoenolpyruvate addition restored all of these activities. These results support a mechanism in which the relative proportions of phosphorylated and nonphosphorylated forms of a phosphotransferase constituent regulate the activity of the lactose permcase.

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