Starch biosynthesis amylose

Erlander, S. R. (1998a). Starch biosynthesis. I. The size distributions of amylose and amylo-pectin and their relationships to the biosynthesis of starch. Starch/Stdrke. 50,227-240. 

All chapters/subjects that were also in the previous edition have been updated. Chapters have been added on the biochemistry and molecular biology of starch biosynthesis, structural transitions and related physical properties of starch, and cyclo-dextrins. There are two chapters on the structural features of starch granules that present not only advances in understanding the organization of starch granules, but also advances in understanding the fine structures of amylose and amylopectin, both of which are based on techniques that have been developed since 1984. 

What roles do the starch synthase isoforms play in the formation of the crystalline starch granule and amylopectin structures How is amylose formed Why are starch granules from different species different in size and in the number per cell New methodology and much effort have resulted in major advances in the understanding of starch biosynthesis, but many questions remain unanswered. Here we discuss some of these open questions and possible answers. 

These reactions do not have to occur in perfect sequence, and the phases may have some overlap (e.g., phases 2, 3, and 4 may overlap, and possibly even 5 and 6). However, the present evidence, such as intermediate products formed by starch mutants of C. reinhardtii and of higher plants, supports the sequence of reactions shown in Fig. 1 for amylopectin and amylose biosynthesis. Further experiments are required to test this hypothetic scheme, and attempts to purify and characterize the debranching enzyme, crucial to this hypothesis, are under way. 

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. 

Interest in the genetic engineering of both plants and micro-organisms for the production of tailor made amylose, amylopectin and/or starches has also been reported. Furthermore, investigations on the enzymatic modification of starch and its major components, for example the introduction of additional branches composed of glucose and/or other monosaccharides and/or uronic acids as well as amino acids or peptides, to produce carbohydrates of possibly comparable functionality to galactomannans, pectin, gum arable, etc., has been initiated. Also studies on the metabolic fate of carbohydrates in food, the biosynthesis of starch, the fine structure of starch from different sources, the effect of electrolytes on the gelatinization of starch and the development of enzymic methods for starch analyses are still active. 

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