Regulation of stromal sedoheptulose 1,7-bisphosphatase activity by pH and Mg2+ concentration.
A scheme is proposed for the regulation of stromal sedoheptulose 1,7-bisphosphatase activity which enlarges upon a previously elaborated mechanism (Woodrow, I.E., and Walker, D.A. (1983) Biochim. Biophys. Acta 722, 508-516). The latter involves oxidized (inactive) and reduced (active) enzyme forms. Both the free enzymes and the enzyme-substrate complexes undergo slow oxidation/reduction. This study examines the behavior of the system under pH and Mg2+ concentration regimes that are likely to occur in the chloroplast stroma. The control of enzyme activity by pH can be described in terms of each free enzyme and enzyme-substrate complex existing in protonated and nonprotonated forms. The molecular dissociation constants for each protonation reaction were calculated from kinetic data. Mg2+ concentration changes modulate these constants. Under conditions that are likely to obtain in the stroma in the dark, the model predicts that approximately 99.1% of the enzyme will be in the inactive forms. Such inactivation is important since it would prevent the reductive pentose phosphate pathway from operating in darkness.
D004789:Enzyme Activation; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology*; D008433:Mathematics; D008954:Models, Biological; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D010944:Plants / Q000201:enzymology*; D011485:Protein Binding; D014908:Triticum / Q000201:enzymology
D010744:Phosphoric Monoester Hydrolases; C022627:sedoheptulose-bisphosphatase; D008274:Magnesium