Inhibition of cytochrome c oxidase and hemolysis caused by lysosphingolipids

Galactosylsphingosine, glucosylsphingosine and sphingosine all inhibited cytochrome c oxidase activity in mitochondria from rat liver; more than 50% inhibition was caused by 5 μM lipid (0.1 μmol/mg mitochondrial protein). However, these lysosphingolipids did not suppress the activity of purified cytochrome c oxidase. When the enzyme was “reconstituted” with phosphatidylcholine, the lysosphingolipids clearly inhibited the activity. On the other hand, galactosylsphingosine, glucosylsphingosine and sphingosine all hemolyzed erythrocytes, indicating that lysosphingolipids can disrupt the membrane. Thus, it appears that the inhibition of cytochrome c oxidase, a membrane-bound enzyme in mitochondria, is due to perturbation of the environment of the enzyme and that the primary attacking site of the lysosphingolipids is the membrane. Because the potency to inhibit cytochrome c oxidase and to hemolyze erythrocytes did not differ among these lysosphingolipids and because galactosylceramide caused neither inhibition of cytochrome c oxidase nor hemolysis, the free amino group in the lysosphingolipids seems to be essential to give the effects. In addition, both inhibition of cytochrome c oxidase and hemolysis caused by lysosphingolipids were completely abolished by albumin, suggesting that toxic effects of lysosphingolipids may not be apparent in blood.