Relationship between the rate of DHR oxidation and iron concentration in plasmalike medium (PLM), normal (N), and thalassemic (TH) sera. The different sera of (TH) and healthy (N) subjects were initially presaturated with iron by mixing with Fe/NTA (5-70 μM as in Figure 3). Fe was then added (as Fe/NTA) to them as well as to samples in PLM. Average DHR oxidation rates (fluorescence units per unit time; FU × minute^-1) were obtained in parallel samples supplemented or not with 50 μM L1 (+L1 and -L1, respectively), their differences calculated and plotted against the concentration of added Fe after subtraction of the basal rate (obtained at 0 added Fe). Linear fit of the compiled data points yielded the slope of 19 ± 1 (r = 0.98) and the respective 95% confidence range (dotted line).