Ordered-disordered domain coexistence in ternary lipid monolayers activates sphingomyelinase by clearing ceramide from the active phase

ELISA CARMEN ALE; BRUNO MAGGIO; MARIA L. FANANI

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2012 vol. 1818 p. 2767 - 2767

e explored the action of sphingomyelinase (SMase) on ternary monolayers containing phosphatidylcholine, sphingomyelin (SM) and dihydrocholesterol, varying along a single tie line of phase coexistence. SMase activity exhibited higher rates and extents of hydrolysis when the film is within the liquid-expanded (LE)/liquid-ordered (LO) coexistence range, compared to monolayers in the full LO phase. Since Alexa-SMase preferably adsorbs to the LE phase, and no direct correlation was found between enzymatic activity and domain borders, we postulate that the LE phase is the active phase for ceramide (Cer) generation. The enzymatically generated Cer organizes in different manners depending on the initial LE/LO ratio. The action of SMase in Chol-poor monolayers leads to the formation of Cer-enriched domains, while in Chol-rich monolayers it results in the incorporation of Cer in the LO phase and formation of new Chol- and Cer-enriched domains. The novel mechanism proposed here provides explanat