Insulin effect on the phospholipid organization and some enzyme activities of rat liver membrane fractions.

1. The influence of insulin on rat liver membrane lipid composition, fluidity, some enzyme activities and asymmetry of microsomal phospholipids were investigated. 2. The total phospholipids and cholesterol were increased in microsomes and reduced in plasma membranes from insulin-treated rats. 3. Of all the investigated enzymes participating in the lipid metabolism, only the neutral sphingomyelinase activity was observed to be enhanced, whereas the ceramide-phosphatidylethanolamine (PE) synthetase and phospholipase A2 activities remained unchanged. 4. Insulin administration caused translocation of phosphatidylserine (PS) and PE to the outer leaflet and of phosphatidylinositol (PI) to the inner leaflet of microsomal membranes.