Characterization and localization of neutral sphingomyelinase in bovine adrenal medulla

Homogenates of bovine adrenal medullae hydrolyzed exogenous Sphingomyelin at 4.3 * 1.6 nmol - mg-' - min-' and 97% of this sphingomyelinase activity was sedimentable at 110,000 g. The sphingomyelinase had a broad pH optimum centered at pH 7. Enzymatic activity was maximal with 80 pM added Mn"; MgZ' supported less than half maximal activity and both Ca2+ and EDTA inhibited activity. No activity was detected in the absence of Triton X-100. Response to detergent was biphasic with dose-dependent stimulation from 0.02% to 0.05% Triton X-100 followed by inhibition with increasing con- centrations of detergent. Activity in response to detergent was also modulated by protein concentration. Sphingomyelinase activity was associated with a plasma membrane-microsomal fraction. Phosphatidylcholine was not hydrolyzed under optimal conditions for sphingomyelin hydrolysis and a variety of other conditions. Neutral-active sphingomyelinase activity in adrenal medulla was similar in magnitude to that observed in other non- neural bovine tissues. 1111 This study demonstrates the presence of a potent neutral-active sphingomyelinase in a plasma mem- brane-microsomal fraction of bovine adrenal medulla. This enzyme may be involved in membrane fusion and lysis during catecholamine secretion through its ability to alter membrane composition. - Bartolf, M., and R. C. Franson. Characteriza- tion and localization of neutral sphingomyelinase in bovine adrenal medulla. J. Lipid Res. 1986. 27: 57-63.