Illustration of the alphabet of the sugar language. Structural representation, name and symbol as well as the set of known acceptor positions (arrows) in glycoconjugates are given for each letter. Four sugars have l- configuration: fucose (6-deoxy-l-galactose), rhamnose (6-deoxy-l-mannose) and arabinose are introduced during chain elongation, whereas l- iduronic acid (IdoA) results from post-synthetic epimerization of glucuronic acid at C-5. The 1C4 conformation of IdoA (a) is in equilibrium with the 2SO form (b) in glycosaminoglycan chains where this uronic acid can be 2-sulfated (please see Figure 7d). All other “letters” are d- sugars. Neu5Ac, one of the more than 50 sialic acids, often terminates sugar chains in animal glycoconjugates. Kdo is a constituent of lipopolysaccharides in the cell walls of Gram-negative bacteria and is also found in cell wall polysaccharides of green algae and higher plants. Foreign to mammalian glycobiochemistry, microbial polysaccharides contain the furanose ring form of d-galactose and also d/l- arabinose indicated by an italic “f” derived from the heterocyclus furan. The α-anomer is prevalent for the pentose arabinose, e. g. in mycobacterial cell wall arabinogalactan and lipoarabinomannan. β1,5/6-Linked galactofuranoside is present in the arabinogalactan and the β1,3/6 linkage in lipopolysaccharides (from , with permission).