The effect of D-alpha-tocopherol on the solubilization of dipalmitoylphosphatidylcholine membrane by anionic detergent sodium dodecyl sulfate

The effect of D-alpha-tocopherol (alpha-T) on phospholipid dipalmitoylphosphatidylcholine (DPPC) membrane solubilization in their gel phase by anionic detergent sodium dodecyl sulfate has been studied using fluorescence spectroscopy, turbidometric and optical microscopy methods. The solubilization process of DPPC occurs in the range of seconds, whereas the equilibration of the resulting mixed micelles occurs over a much longer timescale. The turbidity changes reflecting the membrane solubilization depended on the D-alpha-T/DPPC ratios and detergent concentration. Increasing alpha-T concentration embedded into DPPC membrane, up to 10 mol%, decreases the solubility of the membrane by 45%. Endogenous alpha-T fluorescence indicated that during solubilization, the formation of detergent/alpha-T/phosphatidylcholine aggregates occurred, which led to the mixed micelle formation. Images of the vesicles obtained by optical micros copy visualized that DPPC membrane solubilization and showed that the presence of alpha-T in the membrane increases its resistance to detergent solubilization. The observed processes were discussed on the basis of the hydrophobic-hydrophilic balance in the bilayer.