title: The effect of organic solvents on the activation and the activity of spinach chloroplast fructose-1,6-bisphosphatase.
abstract: A two-stage assay was used to study the effect of organic solvents on the activation of and the catalysis by chloroplast fructose-1,6-bisphosphatase. Irrespective of chemical structure, all the organic solvents tested had a dual effect on the enzyme. In the activation they stimulated and inhibited at low and high concentrations, respectively, in a process that required dithiothreitol, fructose 1,6-bisphosphate, and Ca2+. Conversely, organic solvents inhibited catalysis. The enhancement in fructose-1,6-bisphosphatase activity did not arise from a change in the molecular weight of the enzyme and correlated positively with the hydrophobic character of the organic solvent. In the presence of 2-propanol, all the activation constants for modulators (fructose 1,6-bisphosphate, a2+, thioredoxin-f) were lower than in a strictly aqueous medium. Monothiols were also functional in the activation of chloroplast fructose-1,6-bisphosphatase, although they were less effective than dithiols. Sulfhydryl compounds decreased the concentration of fructose 1,6-bisphosphate required for the activation of the enzyme, and 2-propanol lowered this requirement further. Arrhenius plots were nonlinear for the enzyme activation and linear for the hydrolytic step. The anomalous temperature dependence of the chloroplast fructose-1,6-bisphosphatase activation was indicative of a cooperative process. The data obtained in this study indicate that the concerted activation of chloroplast fructose-1,6-bisphosphatase is favored in a medium less polar than water.
authors.forename: E
authors.initials: E
authors.lastname: Corley
authors.forename: R A
authors.initials: RA
authors.lastname: Wolosiuk
mesh_terms: D000433:1-Propanol / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D054479:Chloroplast Thioredoxins; D002736:Chloroplasts / Q000201:enzymology*; D004229:Dithiothreitol / Q000494:pharmacology; D004789:Enzyme Activation; D006597:Fructose-Bisphosphatase / Q000378:metabolism*; D005635:Fructosediphosphates / Q000494:pharmacology; D010940:Plant Proteins / Q000494:pharmacology; D012997:Solvents / Q000494:pharmacology*; D013696:Temperature; D013879:Thioredoxins
chemical_list: D054479:Chloroplast Thioredoxins; D005635:Fructosediphosphates; D010940:Plant Proteins; D012997:Solvents; D013879:Thioredoxins; D000433:1-Propanol; D006597:Fructose-Bisphosphatase; C029063:fructose-1,6-diphosphate; D002118:Calcium; D004229:Dithiothreitol