The isolation of a membrane-bound protein associated with the β-galactoside-permease of Escherichia coli

Four variations of a dual-isotopic labeling technique are employed for the specific labeling, in vivo, of a membrane-bound component associated with the β-galactoside-permease In E.coli. A procedure for the solubilization of cartain membrane-bound proteins is described. When the membrane extract from a mixture of two cultures where neither culture was grown in the presence of inducer was chromatographed, the ratio of counts, one isotope to the other, remained constant. When both cultures were grown in the presence of gratuitous inducer. the ratio was again constant. However, when only one culture was grown along with inducer, a peak of isotope enrichment was found in the eluate in an area close to the effluent volume for bovine serum albumin. The enriched isotope was that which was added to the induced culture.