Melibiose transport of Escherichia coli

Abstract

Transport of [3H]melibiose, prepared from [3H]raffinose, was investigated in E. coli. Na+ stimulated the transport of melibiose via the melibiose system, whereas Li+ inhibited it. Kinetic parameters of melibiose transport were determined. The Kt values were 0.57 mM in the absence of Na+ or Li+, 0.27 mM in the presence of 10 mM NaCl and 0.29 mM in the presence of 10 mM LiCl. The Vmax values were 40 and 46 nmol/min per mg of protein in the absence and in the presence of NaCl and 18 nmol/min per mg of protein in the presence of LiCl. Melibiose transport via the melibiose system was temperature-sensitive in a wild-type strain of E. coli and was not inhibited by lactose. Melibiose uptake via the lactose system was not temperature-sensitive, was inhibited by lactose and was not affected by Na+ and Li+. Methyl-.beta.-D-thiogalactoside, a substrate for both systems, inhibited the transport of melibiose via both systems.