Partitioning of Triton X-100, deoxycholate and C(10)EO(8) into bilayers composed of native and hydrogenated egg yolk sphingomyelin.

We have used isothermal titration calorimetry (ITC) to study the thermodynamics of Triton X-100 (T(X-100)), deoxycholate and decyl octaethylene glycol (C(10)EO(8)) penetration into bilayers composed of native (ESM) and hydrogenated egg yolk sphingomyelin (DHSM). Light scattering measurements were used to study the point of saturation (R(e,sat)) and the onset of solubilization of membranes by the detergents. We found that DHSM bilayers at 25 degrees C were much more resistant to detergent partitioning (lower K) and gave higher reaction enthalpies (DeltaH) for all three detergents compared to the ESM bilayer system. Because DHSM lacks double bonds (Delta(4trans) and some cis bonds as well), attractive acyl chain interactions are favored in membranes of this lipid class. The high stability and cohesion of DHSM in membranes could be a crucial functional property of this lipid as it is enriched in eye lens membranes.