Reconstitution of LAC carrier function in cholate-extracted membranes from Escherichia coli.

Extraction of $\text{Escherichia}\text{coli}$ ML 308-225 membrane vesicles with cholate yields a particulate fraction containing 10 to 15% of the phospholipid and about 70% of the protein of intact vesicles. Addition of phospholipid to the particulate fraction in the presence of cholate, followed by sonication and removal of detergent by gel filtration yields a vesicular preparation that exhibits $\text{lac}$ carrier function as judged by transient increases in 6′-(N-dansyl)aminohexyl-1-thio-β-D-galactopyranoside fluorescence in the presence of either a lactose diffusion gradient or an artificially-generated membrane potential (interior negative). Activity is not observed in the absence of phospholipid, in the presence of N-ethylmaleimide or in analogous preparations from ML 30 vesicles that do not contain the β-galactoside transport system.