Figure 2.

Effect of histidine concentration on formation and decomposition of the blue complex. For A–D, reaction mixtures (1 ml) contained 20 mM Hepes buffer (pH 7.6), 380 μM Fz, 100 μM FeSO₄, and various concentrations (2–50 mM) of histidine as indicated by the numbers in the panel. For E–H, the reaction mixtures contained 150 μM Fz and 50 μM FeSO₄. Spectral changes were initiated and monitored as described in Experimental Procedures. The dotted lines represent the spectra obtained immediately after addition of 30 mM H₂O₂ following the 10-min recording. The heavy broken lines in C and E illustrate the calculated difference spectrum obtained by subtracting the 10-min spectrum from the initial (zero-time) spectrum. The initial (zero-time) and 10-min spectra are identified by * and #, respectively.