GLUCOSE ACTIVATION AND METABOLISM THROUGH UDP-GLUCOSE PYROPHOSPHORYLASE IN PLANTS

Recent developments in studies on the characterization of properties and functions of UDP-glucose pyrophosphorylase (UGPase) in plant metabolism are presented. UGPase constitutes a reversible enzymatic step for interconversions between starch and sucrose metabolites, and is responsible for synthesis and metabolism of UDP-glucose, a major form of nucleoside diphosphoglucose in plant cells. The enzyme, although considered not to have any regulatory function, has attracted considerable interest due to its ubiquitous distribution in plants, high activity, especially in sink tissues, and because of the key role of UDP-glucose as a direct or indirect precursor of sucrose, starch and structural polysaccharides. The enzyme has been the subject of biotechnological manipulations to engineer its kinetic properties and gene expression in relation to metabolic processes at the sucrose/starch interface. Depending on tissue type, the UGPase reaction may be channelled in vivo, either toward UDP-glucose pyrophosphorolysis or synthesis, due to a metabolic coupling to other reactions of sugar pathways. Some strategies for future research on plant UGPase are discussed.