Characterization of plasma membrane domains enriched in lipid metabolites.

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Abstract
A subpopulation of plasma membrane vesicles enriched in membrane lipid metabolites has been isolated from petals of carnation flowers and leaves of canola seedlings. This was achieved by immunopurification from a microsomal membrane preparation using region‐specific antibodies raised against a recombinant polypeptide of the plasma membrane H+‐ATPase. The properties of this subpopulation of vesicles were compared with those of purified plasma membrane 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 vesicles. Specifically, the immunopurified vesicles are highly enriched in lipid metabolites, including free fatty acids, diacylglycerol, triacylglycerol and steryl and wax esters, by comparison with the phase‐purified plasma membrane. These findings can be interpreted as indicating that lipid metabolites generated within the plasma membrane effectively phase‐separate by moving laterally through the plane of the membrane to form discrete domains within 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 membrane turnover.