Fig. 4.
Binding of (±)-2-sec-butyl-4,5-dihydrothiazole (SBT) to MUP-I (A) and MUP-IV (B), determined by intrinsic protein fluorescence. Each curve shows the ratio of fluorescence emission intensities at wavelengths of 303 and 337 nm plotted against the total SBT concentration. Protein concentrations were 1.0 μM (MUP-I) and 0.1 μM (MUP-IV), and the excitation wavelength was 228 nm. The fitted binding isotherms yielded Kd values of 2.5±1.9 and 0.32±0.29 μM, respectively. Note that the x-axis scale differs by a factor of 10 between the two panels.