The IIBCG'" transmembrane subunit of the glucose transporter of E coli containing a carboxy-termmal affinity tag consisting of six adjacent histidines was purified by nickel chelate affinity chromatography.The protem was constitutively overexpressed from a high copy number plasmid. 1.5 mg of 95% pure protein was obtained from 5 g (wet weight) cells. 70% ofthe phosphotransferase activity present m cell membranes was recovered. Adsorption to the nickel resin allows dehpidation as well as rapid detergent exchange. The procedure was used to demonstrate exchange of subunits in the IIBCG'C dimer and it helds promise for the Investigation of other protein-protein mteractions Phosphotransferase system: Glucose carrier; Ni' chelate chromatography; Enzyme II: E co/i