Enzymes starch-synthesizing

In spite of these limitations to our complete knowledge of starch biosynthesis, information about the pathway of starch biosynthesis gained from studies of maize endosperm mutants can probably be generalized to other plant species because related mutants have occurred in peas, sorghum, barley, rice and Chlamydomonas, and because the same enzymes are found in starch-synthesizing tissues in other plant species. Variation in the number of isozymes and their developmental expression, and variations in cellular compartmentation, however, could result in a range of pathways with significant differences. 

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. 

P-Enzyme is widely distributed in the plant kingdom, and relatively large amounts are present in many starch-synthesizing cells, so that the in vivo importance of this enzyme has become generally accepted. Nevertheless, this view is not supported by certain experimental observations. For example, P-enzyme action is freely reversible, and amylose synthesis will only occur when the ratio (inorganic phosphate) (a-D-glucosyl phosphate) is less than the equilibrium value [10.8 at pH 5, 6.7 at pH 6, and... 

D-glucosyl pyrophosphate), and from a-D-glucosyl phosphate, to appropriate acceptors has also to be determined. Furthermore, the enzyme systems in the starch-synthesizing algae and protozoa are largely unknown. 

Mukerjea, R., Falconer, D.X, Yoon, S.H., and Robyt, J.F. 2010. Large-scale isolation, fractionation, and purification of soluble starch-synthesizing enzymes starch synthase and branching enzyme from potato tubers. Carbohydrate Research, 345, (11), 1555-1563. 

Naturally occurring polymers—those derived from plants and animals—have been used for many centuries these materials include wood, rubber, cotton, wool, leather, and silk. Other natural polymers, such as proteins, enzymes, starches, and cellulose, are important in biological and physiological processes in plants and animals. Modern scientific research tools have made possible the determination of the molecular structures of this group of materials and the development of numerous polymers that are synthesized from small organic molecules. Many of our useful plastics, rubbers, and fiber materials are synthetic polymers. In fact, since the conclusion of World War II, the field of materials has been virtually revolutionized by the advent of synthetic polymers. The synthetics can be produced inexpensively, and their properties may be managed to the degree that many are superior to their natural counterparts. In some applications, metal and wood parts have been replaced by plastics, which have satisfactory properties and can be produced at a lower cost. 

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. 

In contrast to animals, bacteria such as E. coli synthesize glycogen via ADP-glucose rather than UDP-glucose.88 ADP-glucose is also the glucosyl donor for synthesis of starch in plants. The first step in the biosynthesis (Eq. 20-18) is catalyzed by the enzyme ADP-glucose pyrophosphorylase (named for the reverse reaction). 

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