Reconstitution of the melibiose carrier of Escherichia coli.
Different conditions were studied for optimal solubilization and reconstitution of the melibiose carrier of Escherichia coli. Several alpha- and beta-galactosides, known to be substrates for the melibiose carrier, were found to inhibit [3H]-melibiose uptake by proteoliposomes. In the presence of 10 mM Na+ the Km for melibiose counterflow was 0.42 mM. Melibiose and raffinose were good substrates for counterflow, while thiomethyl-beta-galactoside and p-nitrophenyl-alpha-galactoside were accumulated very poorly. Although the latter two sugars are known to be substrates for the carrier, they showed a very rapid rate of passive diffusion across the liposome membrane. The proton ionophore carbonylcyanidechlorophenylhydrazone had no effect on uptake, suggesting that a proton motive force is not essential for the counterflow phenomenon.
D001693:Biological Transport, Active; D002241:Carbohydrates; D004187:Disaccharides / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D008081:Liposomes; D008553:Melibiose / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000302:isolation & purification / Q000378:metabolism*; D013379:Substrate Specificity; D027981:Symporters
D002241:Carbohydrates; D004187:Disaccharides; D008081:Liposomes; D026901:Membrane Transport Proteins; D027981:Symporters; C021548:melibiose permease; D008553:Melibiose