Amylose synthesis

One of these spontaneous mutants gave rise to the precious sticky rice of Thailand. The sticky rice lacks the starch amylose, which constitutes up to 30% of the total starch in nonsticky rice endosperm. The lack of amylose is due to a mutation in a gene called Waxy, which encodes an enzyme required for amylose synthesis (Sano 1984). Sticky rice is an important culinary and cultural component throughout East Asia and is used in festival foods and desserts. In upland regions of Southeast Asia, it is a staple food in many homes. Ten percent of the rice traded each year is sticky rice. 

Waxy A gene that encodes an enzyme for amylose synthesis. 

Further Studies of Gbss and Isoforms Their Involvement in Both Amylopectin and Amylose Synthesis... 

S9, with higher starch synthase activity, had 36% of the amylose content observed in the nonmutant endosperm, whereas mutant S5, with an even lower starch synthase activity of 32%, had only 21% of the nonmutant maize amylose content. These data further support the view that the waxy protein is involved in amylose synthesis. 

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. 

At 50°C, amylose synthesis using the improved mutant and high sucrose concentration (600 mM) allowed the production of amylose chains twice as long as those obtained by the parental enzyme at 30°C [125, 126],... 

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... 

Further studies of GBSS and iso forms their involvement in both amyiopectin and amylose synthesis... 

Amylose synthesis depends on the concentration of ADP-Glc, as GBSSI has a high for the substrate as compared to the soluble starch synthases. The phosphoglucomutase (PGM)-deficient mutants do make starch but are deficient in amylose, even though GBSS is present. The PGM-deficient mutants can make amylopectin but not amylose as shown by detailed structure studies of the starch accumulated by the algal... 

The formation of dextran was first observed as a troublesome slimy product in sugar manufacturing. The enzyme dextran saccharase produced by bacteria only affects saccharose and liberates fructose with dextran formation. A primer of the kind used in the amylose synthesis is not required. In the formation reaction, a very stable complex SEPi, is formed from the enzyme EPn binding to the dextran polymer and the saccharose S. This then decomposes to form fructose F ... 

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