Journal of Lipid Research, Vol 27, 57-63, Copyright © 1986 by Lipid Research, Inc.
Characterization and localization of neutral sphingomyelinase in bovine adrenal medulla
M Bartolf and RC Franson
Homogenates of bovine adrenal medullae hydrolyzed exogenous sphingomyelin
at 4.3 +/- 1.6 nmol X mg-1 X min-1 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 microM
added Mn2+; Mg2+ 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 concentrations 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. This study demonstrates the presence of a
potent neutral-active sphingomyelinase in a plasma membrane-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.
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