FLUORESCENCE STUDY OF THE EFFECTS OF PH AND MG2+ ON THE CONFORMATION OF FRUCTOSE 1,6-DIPHOSPHATASE FROM SPINACH-CHLOROPLASTS

2-p-Toluidino-naphthalene-6-sulfonate is a sensitive fluorescent reporter group which can be used for the detection of the conformation of fructose I ,6-diphosphatase from spinach chloroplasts. When fructose 1,6-diphosphatase was added to a dilute solution of 2-p-toluidino- naphthalene-6-sulfonate at pH 9·0, the fluorescence intensity gradually increased. At this pH, the enzyme activity decreased at the same rate. However, at neutral pH (7·5), this time-dependent fluorescence change was not observed. In the presence of Mg2+ which is an acti vator of the enzyme, the fluorescence intensity was increased instantly and did not change for 30 mm in the pH range 8·0-9·0. From the concentration dependence of the fluorescence intensity, the dissociation constant for Mg2+ was determined, Kdis=3mM. The effects of pH and Mg2+ on the conformation and activity of chioroplast fructose 1,6-diphosphatase are discussed. © 1979 By The Journal Of Biochemistry.