Biophysical Journal 8: 669-690 (1968)
© 1968 the Biophysical Society

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Spectral Studies of Iron Coordination in Hemeprotein Complexes

Difference Spectroscopy below 250 mµ

ABSTRACT

In order to evaluate the feasibility of observing the spectral behavior of protein groups in the coordination sphere of the iron in hemeproteins, criteria are developed to determine whether or not the application of difference absorption spectroscopy to the study of complex formation will be successful. Absolute absorption spectra, 300-1100 mµ, from bacterial catalase complexes are displayed, and the infrared bands correlated with magnetic susceptibility values of similar complexes of other hemeproteins. Dissociation constants for the formation of cyanide and azide complexes of metmyoglobin, methemoglobin, bacterial catalase, and horseradish peroxidase are given. Difference spectra, 210-280 mµ, are displayed for cyanide and azide complexes of these hemeproteins. A band at 235-241 mµ is found in the difference spectra of all low-spin vs. high-spin complexes. The factors which favor the assignment of this band to a transition involving a histidine residue are presented.