The control of amylose synthesis

Starch granules are composed of two types of glucose polymer, amylose and amylopectin, that differ in size and structure. One of the most intriguing challenges in understanding starch synthesis is to explain the apparently simultaneous synthesis of two such different polymers. One isoform of starch synthase, GBSSI, is responsible for amylose synthesis but can also contribute to amylopectin synthesis. The factors which determine the partitioning of GBSSI activity between these two processes are largely unknown. Understanding the properties of GBSSI and how these differ from the properties of the amylopectin-synthesising isoforms of starch synthase are important to the understanding of the control of amylose synthesis. In this review, we will describe how the synthesis of amylose and amylopectin are integrated and what factors may determine the relative amounts of these two polymers.