FIG. 4.

Salt dependence of the specific GGPS activities in crude protein extracts from control and salt-adapted cells (342 mM NaCl) of the WT and mutant ΔGK2 of Synechocystis as well as GGPS protein obtained after overexpression in E. coli. The overexpressed GGPS protein was taken directly after purification (buffer containing 20 mM Na phosphate, 500 mM NaCl, and 300 mM imidazole [pH 7.8]) or after extensive dialyzation (buffer containing 20 mM Tris-maleate and 5 mM MgCl₂ [pH 7.8]). Enzyme assays were performed in NaCl-free or NaCl-containing (342 mM NaCl) buffer. Radioactivity of the GG spots was determined with a phosphoimager and is expressed as pixel intensities per area (PSL). Means ± standard deviations of values are shown. An asterisk indicates specific activities of the overexpressed protein that were divided by the factor 1,000.