Isolation of plasma membranes from mammary gland by two-phase polymer partitioning.

An aqueous polymer two phase partition method was adapted for isolation of plasma membranes from mammary gland of lactating rats. Plasma membranes isolated by this method were enriched 23-fold in activity of the plasma membrane marker phosphodiesterase I and were depleted, relative to homogenates, in activities of enzymes which are markers for intracellular organelles and endomembranes. Yields of plasma membranes obtained by this method were 0.3 +/- 0.1 mg protein/g wet tissue weight. Plasma membranes were isolated more rapidly and yields were more consistent than those obtained with density gradient centrifugation methods which have been applied for isolation of plasma membranes from mammary gland.