Sphingomyelinase of chicken erythrocyte membranes

Most of the chicken erythrocyte's sphingomyelin is hydrolyzed when the chicken red blood cells are incubated in hypotonie solution at 37 °C. Addition of detergents, such as Triton X-100 or Na-cholate, is essential for hydrolysis of external [³H ]sphingomyelin by the erythrocyte membranes. Pure plasma membranes show relatively high sphingomyelinase activity while no activity could be detected in the soluble fraction of the cells. Mg²⁺ and Mn²⁺ activate the enzyme while Ca²⁺ and EDTA strongly inhibit its activity. The optimal pH of the membrane-bound sphingomyelinase lies between pH 7.0-9.0. The detergents Triton X-100 and Na-cholate, at concentrations of 0.5% ( w v) solubilize the membrane-bound enzyme. Human erythrocytes fail to exhibit sphingomyelinase activity. The correlation between the sphingomyelinase activity and its localization is discussed.