Characterization of plasma membrane domains enriched in lipid metabolites

A subpopulation of plasma membrane vesicles enriched in membrane lipid meta bolites has been isolated from petals of carnation flowers and leaves of ca nola seedlings, This was achieved by immunopurification from a microsomal m embrane preparation using region-specific antibodies raised against a recom binant polypeptide df the plasma membrane H+-ATPase, The properties of this subpopulation of vesicles were compared with those of purified plasma memb rane isolated by partitioning in an aqueous dextran-polyethylene glycol two -phase system. The lipid composition of the immunopurified vesicles proved to be clearly distinguishable from that of phase-purified plasma membrane, indicating that they represent a unique subpopulation of plasma membrane ve sicles. Specifically, the immunopurified vesicles are highly enriched in li pid metabolites, including free fatty acids, diacylglycerol, triacylglycero l and steryl and wax esters, by comparison with the phase-purified plasma m embrane. These findings can be interpreted as indicating that lipid metabol ites generated within the plasma membrane effectively phase-separate by mov ing laterally through the plane of the membrane to form discrete domains wi thin the bilayer, It is also apparent that these domains, once formed, are released as vesicles into the cytosol, presumably by microvesiculation from the surface of the plasmalemma, Such removal may be part of normal membran e turnover.