Progress in understanding the biosynthesis of amylose

The storage of glucose in insoluble granules is a distinctive feature of pl ant cells, Biosynthesis of amylose, the minor low molecular mass fraction o f starch occurs from ADP-glucose. This takes place within the polysaccharid e matrix through the action of granule-bound starch synthase, the major pro tein associated with the granule. Recently, amylose has been successfully s ynthesized in vitro from purified granules. Two models have been proposed t o explain the mechanism of amylose synthesis in plants, The first calls for priming of synthesis through small-size malto-oligosaccharides. The second suggests that glucans are extended by granule-bound starch synthase from a high molecular mass primer present within the granule. This extension is t erminated through cleavage to produce amylose, This process is subsequently repeated to give several rounds of amylose synthesis.