Figure 2: Pyoverdine does not bind to NGAL. The binding of pyoverdine and enterobactin to NGAL was measured by a tryptophan fluorescence-quenching method [13, 15]. Siderophore dilutions were preincubated with recombinant human NGAL (2 M) for 30 min prior to reading with a plate reader. (a) Optimization of intrinsic tryptophan fluorescence quenching in rhNGAL by Ferric-DHBA complexes in a dose-dependent manner. (b) Percent of reduction in tryptophan fluorescence upon enterobactin binding to NGAL compared to apo-pyoverdine and ferric pyoverdine. Error bars (some smaller than the symbol) represent ±SD from the average of triplicate readouts at each point.