A Sphingomyelin Transfer Protein in Rat Tumors and Fetal Liver

Abstract

Affinity resins containing covalently bound phospholipids were used to compare the affinity of the phosphatidylcholine transfer protein from bovine liver and a low-specificity lipid transfer protein from rat hepatoma 27 to phosphatidylcholine and sphingomyelin. Binding experiments demonstrated that the bovine liver protein associates specifically with immobilized phosphatidylcholine whereas the hepatoma protein showed a preference for sphingomyelin. Purified antiserum raised against the hepatoma sphingomyelin transfer protein was used to determine the presence of that protein in the cytosol of various experimental tumors as well as in those of normal, regenerating and fetal rat liver. The protein was well expressed in all the tumors examined and in fetal liver as determined by immunodiffusion whereas only minute amounts could be detected in normal liver and in 30-h regenerated liver. The presence of the sphingomyelin transfer protein in cytosol was in parallel with the presence of sphingomyelin in the corresponding mitochondria. The occurrence of sphingomyelin in tumor and fetal liver mitochondria may be due to protein-catalyzed sphingomyelin transfer from the endoplasmic reticulum.