期刊
CHEMISTRY AND PHYSICS OF LIPIDS
卷 130, 期 2, 页码 127-134出版社
ELSEVIER IRELAND LTD
DOI: 10.1016/j.chemphyslip.2004.02.003
关键词
sphingomyelinase; cholesterol; liquid-ordered phases; lipid phase transitions; rafts
Bacillus cereus sphingomyelinase activity was assayed on large unilamellar vesicles composed of sphingomyelin (SM)/cholesterol (Ch) mixtures at varying proportions. Natural (egg) SM was used with a gel-fluid transition temperature at ca. 40degreesC. When the enzyme was assayed at 37 degreesC, the activity on pure SM was exceedingly low, but a small increase was observed as soon as some Ch was added, and a large enhancement of activity occurred with Ch proportions above 25 mol%. The data were interpreted in terms of sphingomyelinase activity being higher in the cholesterol-induced liquid-ordered phase than in the gel phase. The abrupt increase in activity above 25 mol% Ch would occur as a result of a change in domain connectivity, when the Ch-rich liquid-ordered domains coalesced. In equimolar SM/Ch mixtures, that were in the liquid-ordered state in a wide range of temperatures, sphingomyelinase activity was virtually constant in the 30-70degreesC range. The results demonstrate that at the mammalian and bird physiological temperatures Ch modulates sphingomyelinase activity, and that this can occur precisely because most SM have a gel-fluid transition temperature above the physiological temperature range. In addition, Ch activation of sphingomyelinase and the strong affinity of Ch for SM allow the rapid, localised and self-contained production of the metabolic signal ceramide in specific microdomains (rafts). (C) 2004 Elsevier Ireland Ltd. All rights reserved.
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