Figure 3.
A, spectrophotometric titration of the ferrous hERG3-eag–heme complex with CO. Inset, quadratic (Morrison) fitting to the binding curve to give Kd = 1.03 ± 0.37 μm. B, formation of a heme–NO–hERG3 complex (λmax = 390 nm) on dissociation of CO from the ferrous heme–hERG3 complex (3 μm, λmax = 421 nm) in the presence of NO. NO was formed from the NO releasing molecule, S-nitroso-N-acetyl penicillamine (see “Experimental procedures”). Inset, the 421-nm time course, fitted to a three-exponential process; using the dominant (50%) phase a rate constant for dissociation of CO, koff(CO), was determined (koff(CO) = 0.03 s−1).