Partial purification of the Na+-dependent D-glucose transport system from renal brush border membranes

A membrane extract enriched with the Na+ -dependent D-glucose transport system was obtained by differential cholate solubilization of rat renal brush border membranes in the presence of 120 mM Na+ ions. Sodium ions were essential in stabilizing the transport system during cholate treatment. This membrane extract was further purified with respect to its Na+-coupled D-glucose transport activity and protein content by the use of asolectin-equilibrated hydroxylapatite. The reconstituted proteoliposomes prepared from this purified fraction showed a transient accumulation of D-glucose in response to a Na+ gradient. The observed rate of Na+-coupled D-glucose uptake by the proteoliposomes represented about a sevenfold increase as compared to that of the reconstituted system derived from an initial 1.2% cholate extract of the membranes. Other Na+-coupled transport systems such as L-alanine, alpha -ketoglutarate and phosphate were not detected in these reconstituted proteoliposomes.