Amylopectin granule bound synthases

Delrue, B., Fontaine, T., Routier, F., Decq. A., Wieruszeski, J.-M., Van Den Koomhuyse, N., Maddelein, M.-L., Fournet, B., and Ball, S. 1992. Waxy Chlamydomonas reinhardtii Monocellular algal mutants defective in amylose synthesis and granule-bound starch synthase activity accumulate a structurally modified amylopectin. J. BacterioL 174,3612-3620. 

Isozymes of plant starch synthases (2, 16-20) and branching enzymes (2, 16, 21-26) have been characterized. Presumably, they play distinct roles in amylopectin and amylose synthesis. Also, plant and Chlamydomonas reinhardtii granule-bound starch synthases (27-33) are responsible for synthesis of amylose. Mutants defective in this enzyme are known as waxy mutants and contain starch granules that have little or no amylose. 

Chlamydomonas reinhardtii monocellular algal mutants defective in amylose biosynthesis and granule-bound starch synthase activity accumulate a structurally modified amylopectin. J. Bac-teriol. 1992 174 3612-3620. 

Genetically modiHed (anti-GBSS) potato. Potato starch consists of two components amylose (20%) and amylopectin (80%). Granule-bound starch synthase (GBSS) is the major enzyme involved in the formation of amylose. 

Amylose is synthesized by granular-bound starch synthase, whereas amylopectin is synthesized by soluble starch synthase (Chapter 4).334,339 Because amylose is synthesized by the granular-bound starch synthase in a progressive manner,340 the amylose molecule is likely confined in the granule and has little opportunity to interact and form double helices with other starch molecules to facilitate branch formation. Branching reactions do occur on some amylose molecules, but at a much lower frequency than with amylopectin, and result in slightly branched amylose molecules. 

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