Analysis of L-methionine binding to MetQ.

<p>(A) Using tryptophan fluorescence spectroscopy: MetQ (0.05 µM) in 50 mM potassium phosphate pH 8 was excited at 280 nm at 37°C. Example titration of the MetQ signal change at 342 nm with increasing concentrations of L-methionine. (B) Binding isotherms for the interaction of MetQ with L-methionine. The top panel display heat changes upon injection of ligand and the low panel the integrated hears of injection (▪) and the best fit (solid line) to a single site binding model. (C) Radioactive uptake of ¹⁴C-methionine expressed as nmol/mg protein over time in minutes by the wild-type (circles, 50 µM of methionine added) and <i>ΔmetQ</i> (open triangles 50 µM of methionine added, filled triangles 750 µM of methionine added) <i>S. pneumoniae</i> strains.