FIGURE 6.
Bioluminescence color-shift assay to show the ionic strength dependence of the clytin-cgGFP energy transfer measured as KET. Bioluminescence spectra of clytin were obtained upon titration with cgGFP (0–3.62 μm; dark blue line, 0 μm; gray line, 0.03 μm; purple line, 0.06 μm; dark yellow line, 0.12 μm; red line, 0.24 μm; light blue line, 0.45 μm; light green line, 0.90 μm; dark gray line, 1.81 μm; dark green line, 3.62 μm). Concentration of clytin was 0.47 μm. Spectra were recorded in the buffer containing 20 mm PIPES, pH 7.2, 1 mm MgCl2, 0.5 mm EDTA, and different concentrations of NaCl or KCl, upon injection of CaCl2. Clytin and cgGFP were from a later batch, indicating some uncertainty in the absolute values of KET values.