Starch biosynthesis structure

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. 

Buleon, A., Colonna, R, Planchot, V, and Ball, S. 1998. Starch granules Structure and biosynthesis. Int. J. Biol. Macromol. 23 85-112. 

By using mutants of maize and other species, progress has been made in understanding the pathways and enzymes involved in starch biosynthesis and the fine structure of starch polysaccharides. However, starch biosynthesis (Chapter 4) and granule formation are still not completely understood. Thus, integration of the information on polysaccharide biosynthesis (Section 3.6) with that on mutant effects (Section 3.7), is necessary to fully understand polysaccharide biosynthesis and to delineate the limits of this knowledge. 

Mutations of SSIIa have been observed in wheat and rice.208 In wheat, each of the three wheat genomes were mutated to entirely eliminate expression of the SSIIa gene product, Sgp-1 protein in one line 209 the result was reduced starch amounts and an altered starch structure. In rice, two classes of starch have been found. In Indica rices, the starch is of the long chain variety, while in Japonica, it is of the short chain variety.208 Genetic analysis showed that the mutation in Japonica rice led to a loss of starch synthase II.209 Thus, in higher plants, it seems that loss of SSII activity in dicots and SSIIa activity in monocots have the same results with respect to reduced starch content, due to a lowered amount of amylopectin and altered amylopectin chain size distribution. Thus, these genes may have the same function in starch biosynthesis. 

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. 

Glycogenin, the autocatalytic initiator of starch biosynthesis, catalyses the initial glycosylation of one of its own tyrosine residues, followed by the first few a-glucosyl residues of the starch molecule the stereochemistry of the transfer to tyrosine is unknown, but that to the 4-OH of glucose residues is retentive. Again, the X-ray crystal structure revealed no likely nucleophile except Asp 102, which would require a conformation change to be correctly placed." ... 

Structure and Chemistry of the Starch Granule W. Banks and D. D. Muir Starch Biosynthesis and Degradation Jack Preiss and Carolyn Levi Conformation and Behavior of Polysaccharides in Solution David A. Brant... 

Martin, C. Smith, A. M. (1995). Starch Biosynthesis. The Plant Cell, 7, 971-985. Tang, H., Watanabe, K. Mitsunaga, T. (2002). Characterization of Storage Starches from Quinoa, Barley and Adzuki Seeds. Carbohydrate Polymers, 49, 13-22 [91] Tang, H., Watanabe, K. Mitsunaga, T. (2002). Structure and Functionality of Large, Medium and Small Granule Starches in Normal and Waxy Barley Endosperms. Carbohydrate Polymers, 49, 217-224. 

One example of a naturally occurring diazirine, duazomycin A (137 Scheme 11.20), has been reported, isolated in 1985 from a Streptomyces species during a screen for herbicidal compounds [196], It was fotind to inhibit de novo starch synthesis and it was suggested that this is due to direct inhibition of protein synthesis. Duazomycin A is structurally related to 6-diazo-5-oxo-L-norleucine (138), also reported as a natural product from Streptomyces [197], which acts as a glutamine antagonist and inhibits purine biosynthesis [198],... 

Functionally, starch can be considered as a polysaccharide synthesized in a manner permitting its efficient degradation. Hence, biosynthesis of the starch granule is a delicate balance between efficient packing of the glucan chains and the possibility of breaking these structures at degradation. To complete this enzymatically catalyzed process in the potato tuber, a multitude of different enzyme activities are required. 

CGTases (EC 2.4.1.19) are bacterial enzymes that facilitate the biosynthesis of cyclodextrins from starch through intramolecular transglucosylation. The primary structures of most of these enzymes have been published, and the three-dimensional structure of Bacillus circulans CGTase has been established. Studies of transglucosylation molecular mechanism have indicated that amino acids such as histidine and tryptophan are implicated in such mechanisms. Nitration of CGTase with TNM induces a loss of enzyme activity, a decrease in enzyme affinity towards the (i-CD copolymer, and a loss of tryptophan fluorescence (Villette etal. 1993). 

Kram, A. 1995. Structure and Biosynthesis of Starch The Localization of Starch Synthesizing Enzymes with the Use of Immunoelectron Microscopy. PhD thesis. University of Groningen, The Netherlands. 

Nakamura, Y.. Umemoto, T., Takahata, Y., Komae, K., Amano, E., and Satoh, H. 19%b. Changes in structure of starch and enzyme activities affected by sugary mutation in developing rice endosperm Possible role of starch debranching enzyme in amylopectin biosynthesis. Physiol. Plant. 

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. 

This extraordinary structure leads to an understanding of some important mechanisms in the biosynthesis of starch. There is evidence for formation of a so-called "coacervate", in other words a phase separation. The tendency of imits like those shown in Fig. 8.4 to crystallise is obvious - the possibility of close-packing of adjacent units exists, as well as close packing within each imit. A direct consequence of lateral packing of such units is that the enzyme... 

In the plant kingdom, the biosynthesis of the starch granule remains the outstanding subject for investigation. This includes the mode of synthesis of the starch components, the variation in their proportion in different plants, and the occurrence of minor structural features (for example, phosphate groups and n-fructose residues). The relative importance of the enzymes catalyzing n-glucosyl transfer from uridine- and adenosine... 

A dramatic rise of the cost for liquid and gaseous hydrocarbons stimulates development of novel biopolymers which production is not depended on fossil fuels. Fermentative biosynthesis of poly(3-hydroxybutyrate) [PHB] and its homologues - poly(3-hydroxyalkonoates) [PHAs] bases on using renewable organic substrates. Hydrocarbons wastes of food- and wine/juice industries (sugars, melissa, starch et al.) present the basic structural material for bacterial PHB (and PHA). Utilization of hydrocarbons dining biosynthesis of PHA is favorable to eco-efficiency. 

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