Topic 15.2 - transferases with two catalytic sites for...

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Plant Physiology Online: Molecular Model for the Synthesis of Cellulose and Other Wall Polysaccharides That Consist of a Disaccharide Repeat http://4e.plantphys.net/article.php?ch=15&id=33[8/28/2009 8:29:36 AM] A Companion to Plant Physiology, Fourth Edition by Lincoln Taiz and Eduardo Zeiger Topics Essays Study Questions Readings Help Select Chapter: Search HOME :: CHAPTER 15 :: Topic 15.2 PREVIOUS :: NEXT Topic 15.2 Molecular Model for the Synthesis of Cellulose and Other Wall Polysaccharides That Consist of a Disaccharide Repeat Cellulose synthase contains two binding sites for UDP-glucose (or other sugar nucleotides) (Web Figure 15.2.A). After binding UDP-glucose (step 2), the sugars are transferred to the nonreducing end of the glucan (step 3). At step 4, the glucan chain is translocated by two glucose residues, restoring the complex for the start of another round of synthesis (step 1). (Koyama et al. 1997.) These genes code for glycosyl
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Unformatted text preview: transferases with two catalytic sites for transferring glycosyl residues from their nucleotide donors to the nascent polymer acceptor. This two-site arrangement may explain why the cellobiose disaccharide is the repeating subunit in cellulose: It has been proposed that two glucose residues are added to the glucan chain for each catalytic cycle of the enzyme. A similar arrangement in other polysaccharide synthases could explain why disaccharide repeats commonly make up the backbones of many other cell wall polysaccharides in plants. (Click image to enlarge.) Plant Physiology Online: Molecular Model for the Synthesis of Cellulose and Other Wall Polysaccharides That Consist of a Disaccharide Repeat http://4e.plantphys.net/article.php?ch=15&id=33[8/28/2009 8:29:36 AM] Web Figure 15.2.A (Click image to enlarge.) HOME :: CHAPTER 15 :: Topic 15.2 PREVIOUS :: NEXT...
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