Glyco-Chemistry Cycle System Based on Glycosidases

Abstract

Carbohydrates are photosynthesized using carbon dioxide and water and are the most widely distributed organic compounds as biomass on earth. Almost all naturally occurring carbohydrates exist as glycosidic compounds; they include oligo- or polysaccharides, glycolipids, glycoproteins, and nucleosides. In the biosynthesis of these compounds, the glycosidic bonds cannot be formed by the direct dehydration reactions of saccharide units and its aglycon parts. It is necessary to activate the anomeric center of the saccharide unit by introducing an appropriate leaving group so that the anomeric carbon atom is attacked by a hydroxyl group of the aglycon part (Shoda 2001). Catalysts responsible for the glycosylation of these activated saccharides are synthases, which are classified as glycosyl transferases. After being utilized, these glycosidic compounds are finally converted to carbon dioxide and water via combustion or degradation catalyzed by glycosides from bacteria. It is, therefore, obvious that two kinds of enzymes, glycosyl transferases and glycosidases, are involved in the process of glycosylation and deglycosylation in nature, constructing a large carbon cycle system.