On the character and functions of sphingolipids.

Sphingolipids form a large group of membrane lipids showing a diversity of molecular species. Specific functions associated with the saccharide part of glycosphingolipids including co-receptor functions, cell homing phenomena, and attachment by microbes and microbial toxins may not be unique for sphingolipids. However, there are saccharides which appear only in ceramide-bound form and not in other glycoconjugates, and such glycolipids have often been selected as attachment sites by microbes. During the last few years convincing evidence has been presented in favor of ceramide and sphingosine being signaling molecules for various cell functions. The influence of sphingolipids (ceramide) on the properties of the membrane bilayer is still largely unknown. However, based on the structure of ceramide and some experimental evidence one may formulate its role in membrane stability and barrier properties determined by hydrogen bonding in the amide region of ceramide. Furthermore, a natural variation in the number of hydroxyl groups (of fatty acid and long-chain base) may be important for regulation of the potential hydrogen bonds.