Ultrasensitive Behavior in the Synthesis of Storage Polysaccharides in Cyanobacteria

DIEGO FABIAN GOMEZ CASATI; AON, M.; CORTASSA, S.; IGLESIAS, A.

PLANTA

Springer-Verlag

Año: 2003 vol. 216 p. 969 - 975

0032-0935

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. Go´ mez Casatiet al. (2000) Biochem J 350:139–147]. In the present work we show, experimentally and with a mathematical model, that a-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 storagepolysaccharide 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.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. Go´ mez Casatiet al. (2000) Biochem J 350:139–147]. In the present work we show, experimentally and with a mathematical model, that a-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 storagepolysaccharide 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.a-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 storagepolysaccharide 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.