Difference absorption spectra of the heme-HugZ and NADPH cytochrome P450 reductase reaction in the presence of myoglobin. The reference and sample cuvettes contained the hemin-HugZ complex (20 μM), recombinant human NADPH reductase (100 μg) and NADPH (100 μM). The reaction was blanked immediately after the addition of NADPH, and myoglobin (125 μM) was added to the sample cuvette. The shift in the Soret band from 411 to 421 nm was monitored at 1-min intervals for 10 min. The data are representative of three independent experiments.