Inability of the NS-N1-MD-N^IsdC fusion protein to rapidly acquire heme from metHb.

<p>(A) Overlay of the absorption spectra of holo-NS-N1-MD-N^IsdC and holo-IsdC. (B) No shift in the spectrum of a mixture of 3.0 µM metHb heme and 30 µM apo-NS-N1-MD-N^IsdC at the indicated times after mixing in a stopped-flow spectrophotometer. (C) Shift of absorption spectra after mixing 3 µM metHb heme with 30 µM apo-N2 and 30 µM NS-N1-MD-N^IsdC. The arrows indicate the directions of the spectral shift during the reaction. (D) Time course of ΔA₄₀₅ in the 3.0 µM metHb heme/30 µM apo-N2 reactions in the absence and presence of 30 µM NS-N1-MD-N^IsdC.