β‐d‐Galactoside transport in Escherichia coli

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Abstract
The .beta.-D-galactoside transport protein (y-gene product) of Eshcerichia coli, strain T206, was solubilized in 85-95% yield using the organic solvents hexamethylphosphoric triamide at pH 7.5 or butan-1-ol at pH 4.2. The transport protein obtained with the former solvent could be incorporated into a defined lipid/protein aggregate of density 1.12 g/ml, but no .beta.-D-galactoside binding was restored. Diacylglycerol kinase [EC 2.7.1.-] regained activity in the same lipid/protein aggregates. In control experiments, liposomes formed from hexamethylphosphoric triamide were active in the valinomycin-mediated uptake of Rb+ ions. .beta.-D-Galactoside binding (3.6-5.7 nmol/mg protein) as well as diacylglycerol kinase activity [7 nmol min-1 (mg protein)-1] was reconstituted into proteoliposomes from butan-1-ol solution by adaptation of a published procedure. A microparticulate nature of the butan-1-ol-solubilized transport protein could be excluded by gel permeation chromatography on a newly synthesized matrix, hydroxypropyl-Sepharyl S-300.