The maximum solubilities measurements of Cholesterol, Stigmasterol and Ergosterol in lipid membranes

The chemical structure of cholesterol molecule is very similar to that of other sterols, such as plant sterol stigmasterol and yeast/fungi sterol ergosterol. However, mammalian cells universally use cholesterol. Scientists are wondering what makes cholesterol so unique that animal cells prefer cholesterol, not other sterols. We measured the maximum solubilities of cholesterol, stigmasterol and ergosterols (which are one of the abundant sterols in plants and fungi respectively) in the simplest form of lipid membrane, DPPC using anti-correlation light scattering technique. We found that the solubility limit of cholesterol is the highest (67 mol%) among these sterols, and the solubility limits for ergosterol and stigmasterol are 56 mol% and 48 mol%, respectively. Our result shows that a small difference in sterol structure can result in a major difference in the behavior of sterols. The unique high solubility of cholesterol is essential for cholesterol to perform its biological functions in mammalian cells.