Phospholipids of subcellular organelles isolated from cultured BHK cells.

Mitochondrial and nuclei were purified from cultured hamster fibroblasts (BHK21 cells) by centrifugation in sucrose gradients. The phospholipid compositions of the preparations were compared to those of the previously purified plasma membranes, endoplasmic reticulum and lysosomes. The mitochondria had a characteristically high content (approx. 16% of lipid phosphorus) of cardiolipin, which was practically absent from the other purified organelles. The nuclei were enriched in phosphatidylcholine and phosphatidylinositol (approx. 68% and 5% of lipid phosphorus, respectively). Lysobisphosphatidic acid was almost absent from the mitochondria and nuclei, as well as from the plasma membrane and endoplasmic reticulum, which suggests that this phospholipid is confined to the lysosomes of the BHK cell. The nuclei and the mitochondria contained relatively little sphingomyelin, a characteristic lipid of the plasma membrane. The distributions of the total cellular phospholipid and protein between the various organelles were calculated and compared to the corresponding data estimated for the rat liver. The BHK cell contained relatively more phospholipids in the nucleus and the lysosomes than the liver. All the organelles of the BHK cell contained less protein per phospholipid than the equivalent organelles of the liver.