DHR oxidation mediated by mixtures of iron and ascorbate. (A) Samples of plasmalike medium (PLM) containing increasing concentrations of iron (as Fe(III):NTA complex) were mixed with reagent (“Materials and methods”) containing increasing concentrations of ascorbate (0-160 μM) and 50 μM DHR without (no L1) or with (+ L1) 50 μM iron chelator L1. The rate of increase in DHR fluorescence was followed and is given as arbitrary fluorescence units per time (FU × minute^-1). (B) Plot of the L1-sensitive component of DHR oxidation in Graph A (“μDHR oxidation rate”) versus ascorbate concentration. Shown for comparison are 2 concentrations of Fe, 5 and 20 μM (▪ and •, respectively).