ISSN:
1432-2048
Keywords:
CO2 fixation
;
Fructose-1,6-bisphosphatase
;
Photosynthesis
;
Regulation (fructose-1,6-bisphosphatase)
;
Spinacia (chloroplasts)
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract The effect of pH and of Mg2+ concentration on the light activated form of stromal fructose-1,6-bisphosphatase (FBPase) was studied using the enzyme rapidly extracted from illuminated spinach chloroplasts. The (fructose-1,6-bisphosphate4-)(Mg2+) complex has been identified as the substrate of the enzyme. Therefore, changes of pH and Mg2+ concentrations have an immediate effect on the activity of FBPase by shifting the pH and Mg2+ dependent equilibrium concentration of the substrate. In addition, changes of pH and Mg2+ concentration in the assay medium have a delayed effect on FBPase activity. A correlation of the activities observed using different pH and Mg2+ concentrations indicates, that the effect is not a consequence of the pH and Mg2+ concentration as such, but is caused by a shift in the equilibrium concentration of a hypothetical inhibitor fructose-1,6-bisphosphate3- (uncomplexed), resulting in a change of the activation state of the enzyme. The interplay between a rapid effect on the concentration of the substrate and a delayed effect on the activation state enables a rigid control of stromal FBPase by stromal Mg2+ concentrations and pH. Fructose-1,6-bisphosphatase is allosterically inhibited by fructose-6-phosphate in a sigmoidal fashion, allowing a fine control of the enzyme by its product.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00392274
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