A Universal Lipid Exchange Protein from Rat Hepatoma

Abstract

The postmicrosomal protein fraction from rat hepatoma 27 adjusted to pH 5.1 stimulated phospholipid exchange between rat liver microsomes and mitochondria with higher rates and in a less specific way than the corresponding fraction from rat liver. A phospholipid exchange protein was purified to homogeneity from the hepatoma pH-5.1 supernatant by gel filtration on Sephadex G-75 and ion-exchange chromatography on carboxymethylcellulose. The isolated protein had a MW of 11,200 as determined by electrophoresis on polyacrylamide in the presence of dodecyl sulfate and 11,168 as calculated from the amino acid composition. Isoelectric focusing showed a single band at pH 5.2. In the assay system rat liver microsomes .fwdarw. mitochondria the protein exhibits a complete lack of substrate specificity transferring all major microsomal phospholipids to about the same extent. The possible role of the isolated phospholipid exchange protein in the chemical dedifferentiation of hepatoma cell membranes is discussed.