Fig. 5. Selectivity assays of YFP-MetQ-R189CouA mutants containing the indicated mutations against l-Met, d-Met and l-Gln. FRET ratios were calculated from ICouA, 468 nm and IYFP, 537 nm upon excitation at 360 nm, in the presence and the absence of each AA. FRET ratio changes were calculated from eqn (1). Each data-point represents the average of three independent experiments. Assay conditions: 100 nM sensor protein, 50 mM phosphate buffer (pH 9.0), 50 mM NaCl, and AA (indicated concentration).
