any of the monobasic polyhydroxy amino acids that are derivatives of neuraminic acid. Sialic acids are colorless crystalline solids that dissolve readily in water but are insoluble in nonpolar solvents. They decompose without melting in the temperature range 130°-200°C and are easily decomposed by the action of acids and bases. In nature, as components of glycoproteins and glycolipids, sialic acids are found in, among other places, the cell walls of animals, nerve tissue, and mucous secretions. The biosynthesis of biopolymers containing sialic acids is carried out using the activated form of sialic acids, namely, cytidine monophosphate-sialic acids, which are special sialyltransferase enzymes. Sialic acids determine the antigen and receptor properties of cell surfaces, participating in the interaction of the surfaces with, for example, viruses, toxins, and hormones.