An extract of soluble proteins was prepared from a rat kidney brush-border membranes by Triton X-100 solubilization followed by centrifugation for 1 h at 100000g. Its protein composition was markedly different from that of the brush-border membranes. Proteoliposomes were formed by co-sonication of the Triton X-100-free extract with a naturally occurring mixture of phospholipids extracted from rat kidney. These proteoliposomes were shown to contain Na+-stimulated D-glucose-, L-alanine- and phosphate-transport systems.
