title: Ultrasensitive behavior in the synthesis of storage polysaccharides in cyanobacteria.
abstract: The glycogen synthetic pathway operates ultrasensitively as a function of the ADPglucose pyrophosphorylase (ADPGlcPPase) allosteric effectors, 3-phosphoglycerate and Pi, in permeabilized cells of the cyanobacterium Anabaena PCC 7120. In vitro data previously showed that the ultrasensitive behavior of ADPGlcPPase depends upon cross-talk between the two allosteric effectors, the enzyme's response being additionally modulated by molecular crowding [D.F. Gómez Casatiet al. (2000) Biochem J 350:139-147]. In the present work we show, experimentally and with a mathematical model, that alpha-1,4-glucan synthesis is also ultrasensitive in cells due to the propagation of the switch-like behavior of ADPGlcPPase to the synthetic pathway. Amplifications of up to 20-fold in storage-polysaccharide synthesis can be achieved with a modest 6.7-fold increase in 3-phosphoglycerate in the presence of 5 mM Pi in contrast to the 30-fold necessary in its absence. This is the first time that this phenomenon has been reported to occur in the glycogen synthetic pathway of a photosynthetic prokaryote. The implications of the results for plant cell physiology during light-dark transitions are discussed.
authors.affiliation: Instituto Tecnológico de Chascomús (IIB INTECH), Camino de Circunvalación Laguna km 6, CC 164 (7130) Chascomús, Buenos Aires, Argentina.
authors.forename: Diego F
authors.initials: DF
authors.lastname: Gómez-Casati
authors.forename: Sonia
authors.initials: S
authors.lastname: Cortassa
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Aon
authors.forename: Alberto A
authors.initials: AA
authors.lastname: Iglesias
mesh_terms: D000245:Adenosine Diphosphate Glucose / Q000378:metabolism; D017033:Anabaena / Q000201:enzymology / Q000378:metabolism*; D002463:Cell Membrane Permeability; D005936:Glucans / Q000096:biosynthesis*; D051599:Glucose-1-Phosphate Adenylyltransferase; D005958:Glucosephosphates / Q000378:metabolism; D005988:Glyceric Acids / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism; D008954:Models, Biological; D009713:Nucleotidyltransferases / Q000378:metabolism
chemical_list: D005936:Glucans; D005958:Glucosephosphates; D005988:Glyceric Acids; D000245:Adenosine Diphosphate Glucose; C005156:3-phosphoglycerate; D006003:Glycogen; C040088:1,4-glucan; C031590:glucose-1-phosphate; D009713:Nucleotidyltransferases; D051599:Glucose-1-Phosphate Adenylyltransferase