Regulation of Starch Metabolism: the Age of Enlightenment?

Starch and sucrose are the primary products of photosynthesis in the leaves of most plants. Starch represents the major plant storage carbohydrate providing energy during the times of heterotrophic growth. Starch metabolism has been studied extensively, leading to a good knowledge of the numerous enzymes involved. In contrast, understanding of the regulation of starch metabolism is fragmentary. This review summarises briefly the known steps in starch metabolism, highlighting recent discoveries. We also focus on evidence for potential regulatory mechanisms of the enzymes involved. These mechanisms include allosteric regulation by metabolites, redox regulation, protein-protein interactions and reversible protein phosphorylation. Modern systems biology and bioinformatic approaches are uncovering evidence for extensive post-translational protein modifications that may underlie enzyme regulation and identify novel proteins which may be involved in starch metabolism.