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The Source for Glucan Bio Info |
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Uses: |
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Synthesis |
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The pathways of starch, cellulose, mixed-linkage glucan and hemicellulose biosynthesis (see pathway diagram below) have a common metabolic origin: namely that they both utilize nucleotide sugars as the source of carbohydrate for glucan polymerization. These pathways are known to involve the inter-conversion of sugars and sugar-phosphates resulting the formation of nucleotide-sugars which are the essential precursors of the glucans. Additional biopolymer synthesis details are presented in additional pages for starch, cellulose, hemicellulose and mixed-linkage glucans. The first step in the pathway of starch synthesis is the production of ADP-glucose by the enzyme ADP-glucose pyrophosphorylase (AGPase). This enzyme was originally believed to be restricted to the plastid compartment of the cells of all plants. Recently it has been found that in the endosperm of cereal crops, AGPase is located predominantly in the cytosol and ADP-glucose is transported directly into the amyloplasts. In contrast, in the storage organs of other starch-rich crops, AGPase appears to be located exclusively in amyloplasts and hexose phosphate is imported to support ADP-glucose synthesis inside the amyloplasts. In a minor pathway hexose phosphate also is transported in cereal endosperm and converted to ADP-glucose by a second AGPP located within amyloplasts. |
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Synthesis: |
