The action of sphingomyelinase from Bacillus cereus on ATP-depleted bovine erythrocyte membranes and different lipid composition of liposomes

Abstract

The presence of cholesterol or phosphatidylethanolamine in sphingomyelin liposomes enhanced 2- to 10-fold the breakdown of sphingomyelin by sphingomyelinase from Bacillus cereus. On the other hand, the presence of phosphatidylcholine was either without effect or slightly stimulative at a higher molar ratio of phosphatidylcholine to sphingomyelin ( 3 1 ). In the bovine erythrocytes and their ghosts, the increase by 40–50% or the decrease by 10–23% in membranous cholesterol brought about acceleration or deceleration of enzymatic degradation of sphingomyelin by 50 or 40–50%, respectively. The depletion of ATP (<0.9 mg ATP/100 ml packed erythrocytes) enhanced K + leakage from, and hot hemolysis (lysis without cold shock) of, bovine erythrocytes but decelerated the breakdown of sphingomyelin and hot-cold hemolysis (lysis induced by ice-cold shock to sphingomyelinase-treated erythrocytes), either in the presence of 1 m m MgCl 2 alone or in the presence of 1 m m MgCl 2 and 1 m m CaCl 2. Also, ATP depletion enhanced the adsorption of sphingomyelinase onto bovine erythrocyte membranes in the presence of 1 m m CaCl 2 up to 81% of total activity, without appreciable K + leakage and hot or hot-cold hemolysis. These results suggest that the presence of cholesterol or phosphatidyl-ethanolamine in biomembranes makes the membranes more susceptible to the attack of sphingomyelinase from B. cereus and that the segregation of lipids and proteins in the erythrocyte membranes by ATP depletion causes the deceleration of sphingomyelin hydrolysis despite the enhanced enzyme adsorption onto the erythrocyte membranes.