ABSTRACT
Ceramides have been known for decades as intermediates in sphingolipid metabolism and as minor membrane components (Stoel 1971). e most commonly found ceramides, those with a fatty acyl chain of 16 carbon atoms or longer, are among the least polar, most hydrophobic lipids in membranes. Indeed, their hydrophobicity explains their abundance in the stratum corneum, the barrier that prevents water evaporation through the skin (Wertz and Downing 1989). eir solubility in water is negligible. us, free ceramides cannot exist in solution in biological uids or in cytosol. In addition, long-chain ceramides (e.g., with a fatty acid C12 or longer) belong to the category of nonswelling amphiphiles
CONTENTS 7.1 Ceramides: An Introduction 137 7.2 Calorimetric Studies of Pure Ceramides 138 7.3 Mixtures with Phospholipids 141
7.3.1 Ceramide/Glycerophospholipid Mixtures 141 7.3.2 Ceramide in Mixtures with Sphingomyelins 145
7.4 Mixtures with Cholesterol (and Other Lipids) 147 Acknowledgments 149 References 149
(Small 1970), implying that they cannot even give rise to micelles or other aggregates in aqueous suspension, unlike, for example, common phospholipids, glycosphingolipids, and surfactants. Short-chain ceramides (e.g., N-acetyl or C2 ceramide) appear to “swell” in water, giving rise to homogeneous dispersions (Hannun et al. 1987; Simon and Gear 1998) that are treated, in practice, as solutions.
