Properties and regulation of C-1-fructose-1,6-diphosphatase from spinach chloroplasts

Chloroplast fructose diphosphatase (EC 3.1.3.11) was purified according to the procedures of Racker and Schroeder 1] and Buchanan et al. 2] and the properties compared. Neither preparation contained fructose diphosphatase from the cytoplasm. The preparations had similar molecular weights, pH optima, affinities for fructose diphosphate and Mg²⁺ and were similarly activated by EDTA, dithiothreitol and cystamine.Mg²⁺, fructose diphosphate and dithiothreitol all activate chloroplast fructose diphosphatase more so at suboptimal pH values. The combined effects of these substances under estimated physiological conditions in the chloroplast stroma in the light and in darkness were consistent with almost full activity of the enzyme during illumination but no activity in the dark.