Effect of 22R-hydroxycholesterol on the action of sphingomyelinase from Bacillus cereus toward bovine erythrocytes

Abstract

The incorporation of 22R-hydroxycholesterol [(22R)-5-cholestene-3β,22-diol] into the bovine erythrocyte membranes remarkably enhanced the degradation of sphingomyelin in erythrocyte membranes by the action of sphingomyelinase from Bacillus cereus, causing much faster hemolysis of erythrocytes. The stimulative effect of 22R-hydroxycholesterol on the breakdown of sphingomyelin was maximal in the presence of Mg 2+. On the other hand, in spite of the presence of 22R-hydroxycholesterol, the breakdown of sphingomyelin was inhibited by increasing concentrations of Ca 2+. Also, the incorporation of 22R-hydroxycholesterol into the erythrocyte membranes facilitated the specific adsorption of the enzyme onto the surface of the erythrocyte membranes. The specific adsorption of sphingomyelinase amounted to 20–40% of the total activity in the presence of Mg 2+ and the absence of divalent metal ions. In the presence of Ca 2+, the incorporation of 22R-hydroxycholesterol enhanced the enzyme adsorption, exceeding more than 90% of the total activity. Therefore, the incorporation of 22R-hydroxycholesterol into bovine erythrocyte membranes remarkably accelerates the breakdown of sphingomyelin in the presence of Mg 2+, and the specific adsorption of sphingomyelinase onto erythrocytes in the presence of Ca 2+.