Figure 5. Interaction of haem with the IRP2 73aa-Domain studied by absorption spectroscopy and EPR.

(A) Absorption spectra of the truncated peptide in 50 mM phosphate buffer and 0.25 M NaCl (pH 8) in the absence (dotted line) and in the presence of one equivalent of haem (continuous line). The haemin absorption spectrum is shown for reference (discontinuous line). (B) Absorption spectra of the intact peptide with symbols as in (A). Maxima for the haem–peptide complexes are indicated. (C) EPR spectrum in the g≈2 region of the complex between haem and the truncated form of IRP2 73aa-Domain. Microwave frequency 9.655 GHz; microwave power 4 mW; receiver gain 4×10⁵; modulation amplitude 1 mT, temperature 13 K.