Purification of plasma membranes from rat mammary gland by a density perturbation procedure

A highly purified plasma membrane fraction was obtained from a microsomal subfraction of rat mammary gland after treatment with digitonin to increase its density. The purified membranes were enriched 70-fold overall in 5'-nucleotidase with essentially no contamination from glactosyltransferase, succinate-ING reductase, or NADPH-cytochrome c reductase. The membranes were also highly enriched in sialoglycoproteins.