Cell-free transfer of membrane lipids. Evidence for lipid processing.
A latent phospholipase A is concentrated in cis elements of rat liver Golgi apparatus, the presumed sites of fusion of the 50-70-nm transition vesicles formed from endoplasmic reticulum. As a result, conversion of transferred phospholipids to their corresponding lysoforms may provide an index of post transfer lipid processing in a corresponding reconstituted membrane transfer system. To label the phosphatidylcholine of transitional endoplasmic reticulum in vitro, [14C]CDP-choline and endogenous cytidyltransferases were used. In the reconstituted transfer system, the radiolabeled phosphatidylcholine was transferred via transition vesicles to Golgi apparatus immobilized on nitrocellulose strips in a time- and temperature-dependent process. Transfer was promoted by ATP and the ATP-dependent transfer was specific for cis Golgi apparatus elements as acceptor. Trans Golgi apparatus elements were ineffective as acceptors. Median Golgi apparatus elements were intermediate. A portion of the transferred phosphatidylcholine was converted subsequently to lysophosphatidylcholine also in a time- and ATP-dependent manner. The phospholipase A activity of the Golgi apparatus was more than 90% latent (active site located on the lumens of the Golgi apparatus membranes). Therefore, the lipid-containing vesicles derived from endoplasmic reticulum must have combined with cis Golgi apparatus membranes as the basis for Golgi apparatus-dependent phospholipase A processing of endoplasmic reticulum-derived phosphatidylcholine. Since the lipids were processed by phospholipase A in approximately the same proportion as occurs in situ, the findings offer evidence both for the specificity of the ATP-dependent component of cell-free lipid transfer from endoplasmic reticulum to Golgi apparatus and its fidelity to lipid transfer observed in vivo.
Moreau
P
P
Department of Medicinal Chemistry, Purdue University, West Lafayette, Indiana 47907.
Morré
D J
DJ
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002474:Cell-Free System; D006056:Golgi Apparatus / Q000201:enzymology / Q000378:metabolism*; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism; D008244:Lysophosphatidylcholines / Q000378:metabolism; D008297:Male; D008563:Membrane Lipids / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000378:metabolism; D010741:Phospholipases A / Q000378:metabolism; D051381:Rats; D013347:Subcellular Fractions / Q000201:enzymology; D013696:Temperature
D008244:Lysophosphatidylcholines; D008563:Membrane Lipids; D010713:Phosphatidylcholines; D000255:Adenosine Triphosphate; D010741:Phospholipases A