Incorporation of proteins in sphingomyelin-water gel phases.

Sphingomyelin from bovine milk and water form lipid gel phases at room temperature. A sample was used which incorporated of about 55% water, and X-ray diffraction data indicate an aqueous layer thickness of about 28 Angstrom. In order to accommodate proteins in the gel phase, the aqueous layer thickness was increased by solubilizing sodium palmitate into the sphingomyelin bilayer. In this way the gel phase could take up about 80% water. The incorporation of lysozyme, beta-lactoglobulin, and alpha-lactalbumin, was followed and the protein concentration for phase separation to occur was determined. It was found that the degree of incorporation was dependent on the salt concentration, thus the protein used was extensively dialysed. The amount of protein which can be dissolved in the thin aqueous layer of the gel phase was suggested to be limited by the dimensions of the layer. These are likely to be reduced as a consequence of the osmotic stress exerted by the 'outside' solution phase at high enough protein concentration.