Correlation between the thermotropic behavior of sphingomyelin liposomes and sphingomyelin hydrolysis by sphingomyelinase of Staphylococcus aureus

The hydrolysis of d-erythro beef brain sphingomyelin and d,l-erythro-N-palmitoylsphingomyelin dispersed as multilamellar liposomes by sphingomyelinase of Staphylococcus aureus is correlated with the thermotropic behavior of the sphingomyelins. In both cases maximal enzymatic hydrolysis was achieved at the beginning of the gel to liquid crystalline phase transition (30°C for beef brain sphingomyelin and 41°C for N-palmitoylsphingosinephosphorylcholine) with much lower activity both below and above these temperatures. The enzymatic activity was depressed in the presence of cholesterol in the bilayer which also depressed the phase transition. The profile of the enzymatic activity is explained by the uniqueness of the lipid molecules arrangement at the phase transition.