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More than 50 years ago, Blix, Klenk, and other investigators discovered N-Acetylneuraminic acid as a major product relaesed by mild acid hydrolysis of brain glycolipids or salivary mucine. The complete structure, chemistry, and biosynthesis of this molecule were subsequently characterized in the 1950s and 1960s by several group, including those of Gottschalk, Roseman, Brossmer, Warren, Yamakawa, and Glick. Meanwhile, sialic acids emerged as the targets for recognition by influenza viruses. Chargaff's group discovered that the "receptor-destroying enzyme" activity of influenza viruses acts as a sialidase, releasing sialic acids from macromolecules, and Meyer's group found a similar activity in bacterial sources. Early on, it was apparent that this 9-carbon acidic sugar was actually a common member of whole family of compounds related to neuraminic acid. Partly because of their original discovery in salivary mucins, this family was christened the "sialic acids." By the 1980s, more than 30 types of sialic acids has been discovered by Schauer and other investigators, and many were shown to be expressed in a cell-type-specific and developmentally regulated manner. More recently, the discovery of KDN by Inoue and colleagues has further expanded the family of sialic acids.
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