GLUCOSE ACTIVATION AND METABOLISM THROUGH UDP-GLUCOSE PYROPHOSPHORYLASE IN PLANTS

Recent developments in studies on the characterization of properties a nd functions of UDP-glucose pyrophosphorylase (UGPase) in plant metabo lism are presented. UGPase constitutes a reversible enzymatic step for interconversions between starch and sucrose metabolites, and is respo nsible for synthesis and metabolism of UDP-glucose, a major form of nu cleoside diphosphoglucose in plant cells. The enzyme, although conside red not to have any regulatory function, has attracted considerable in terest due to its ubiquitous distribution in plants, high activity, es pecially in sink tissues, and because of the key role of UDP-glucose a s a direct or indirect precursor of sucrose, starch and structural pol ysaccharides. The enzyme has been the subject of biotechnological mani pulations to engineer its kinetic properties and gene expression in re lation to metabolic processes at the sucrose/starch interface. Dependi ng on tissue type, the UGPase reaction may be channelled in vivo, eith er toward UDP-glucose pyrophosphorolysis or synthesis, due to a metabo lic coupling to other reactions of sugar pathways. Some strategies for future research on plant UGPase are discussed.