Comparative studies on membranes from bovine choroid plexus and rat kidney cortex.

Comparative subcellular fractionation studies on rat kidney and bovine choroid plexus using differential centrifugation and free flow electropheresis were undertaken because of the morphological and functional similarities of the epithelial cells of both tissues. The activities of three enzymes commonly used as markers for brush border membranes in kidney were measured in fractions of each tissue. γ-Glutamyl transpeptidase, alkaline phosphatase, and 5'-nucleotidase copurified in membrane fractions of renal cortex collected by differential centrifugation. Application of a similar fractionation procedure to choroid plexus gave relatively similar results, except for alkaline phosphatase, the yield of which was substantially reduced in a fraction enriched with two marker enzymes. Further fractionation of γ-glutamyl transpeptidase and alkaline phosphatase activities in these membrane fractions was achieved using free flow electropheresis. The two enzymes from kidney exhibited discrete peaks with a small separation, while the electropheretic pattern of γ-glutamyl transpeptidase from choroid plexus was biphasic. Alkaline phosphatase was observed to migrate with the more basic γ-glutamyl transpeptidase peak.