title: Properties of freshly purified and thiol-treated spinach chloroplast fructose bisphosphatase.
abstract: Freshly purified spinach chloroplast fructose bisphosphatase is powerfully inhibited by inorganic phosphate competitively with respect to its substrate fructose 1,6-bisphosphate. The concentrations of phosphate and substrate in the chloroplast stroma are such that the enzyme in this form could not operate at a significant rate in vivo. Incubation of the enzyme with dithiothreitol for 24 h decreases the Km for fructose 1,6-bisphosphate from 0.8 to 0.033 mM, decreases the Km for Mg2+ from 9 to 2 mM and substantially alleviates inhibition by inorganic phosphate. The physiological significance of thiol activation of the enzyme is discussed.
mesh_terms: D002736:Chloroplasts / Q000201:enzymology*; D004229:Dithiothreitol / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D006597:Fructose-Bisphosphatase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D010710:Phosphates / Q000494:pharmacology
chemical_list: D010710:Phosphates; D006597:Fructose-Bisphosphatase; D008274:Magnesium; D004229:Dithiothreitol