66] ADP-glucose: α-1,4-glucan glucosyltransferases (starch synthetases and related enzymes) from plants

Abstract

Publisher Summary This chapter discusses the synthesis of α-l,4-glucan glucosyltransferases from plants. Several enzymes found in plants transfer the glucose moiety from adenosine diphosphate (ADP)-glucose to starch granules, amylose, amylopectin, phytoglycogen, and oligosaccharides of the maltose series, forming α-1,4 linkages. Some of these enzymes are fixed to the starch granules and use only malto-oligosaccharides and intact starch grains as acceptors. The enzyme is bound to the starch granule. This permits a separation of enzyme and product from the reaction mixture by simple centrifugation. The enzyme activity is measured by the amount of ADP formed or by incorporation of 14 C-glucose into the starch granules. The reagents used, purification procedure followed, and the steps involved in the preparation of enzyme are also described in the chapter. The maximum activity is found with ADP-glucose, and it is not modified in the presence of other sugar nucleotides. In the assay method of soluble enzyme from sweet corn, the enzyme activity is measured by the amount of ADP formed from ADP-glucose in the presence of phytoglycogen, or by the incorporation of radioactivity from ADP- 14 C-glucose. This method is useful in the case of crude extracts where it is difficult to determine the ADP formed.