Comparison of Bile Salt-Binding Proteins in Basolateral Membranes from Small Intestine, Kidney, and Liver

Abstract

Previous photoaffinity labeling experiments suggested that proteins with apparent molecular weights of 48,000 and 54,000 are components of the Na+-dependent and Na+-independent bile salt transport systems, respectively, in the basolateral (sinusoidal) membrane of rat hepatocytes. In this study we attempted to identify the proteins possibly related to Na+-independent bile salt transport across the basolateral membranes of rat ileal and renal proximal tubule cells and to compare them with the respective proteins from hepatocytes. Basolateral membrane vesicles were prepared from rat ileum and kidney cortex and subjected to photoaffinity labeling with radioactive 3- and 7-diazirine derivatives of taurocholate. Following labeling, membrane proteins were separated by one- and two-dimensional gel electrophoresis and incorporated radioactivity was detected by fluorography and liquid scintillation counting. In basolateral membranes isolated from ileum several polypeptides were labeled with predominant incorporation of radioactivity into a polypeptide of app. MW 54,000. In basolateral membranes from rat kidney cortex also several membrane proteins were labeled.