Isolation of anionic sialoproteins from the rat glomerulus.

The epithelial glomerular polyanion (GPA) designates an array of sialic acid-containing sites along the surface of the glomerular epithelium which react with cationic dyes or probes. In this work, sequential rat glomerular isolation, ultrasonic disruption, trypsin digestion, ion-exchange chromatography, and preparative polyacrylamide gel electrophoresis have been used to isolate anionic sialoglycoproteins from the glomerular epithelium. Because colloidal iron (CI) reactivity has been used to define the GPA histologically, we used a modification of the CI reaction to monitor and direct the isolation procedure. Three major fractions have been recognized and isolated in homogeneity. Antibodies to two of the fractions have been raised by immunization in rabbits. Indirect immunofluorescent and peroxidase-antibody techniques have localized both antigens to the glomerular visceral epithelium of normal rat kidney. This identification and definition of components of the GPA is valuable in delineating a role for GPA in glomerular function.