Abstract
The IR spectra of horse metmyoglobin ligated with the various isotopic forms of the cyanide ion at pH 7.4 display an asymmetric isotope-sensitive profile in the C–N stretching region. Replacement of the water solvent by D 2O or reducing the pH to 5.5 downshift the center frequency of the profiles by ≈1 cm −1 indicating that the Fe–C–N is hydrogen bonded. The measured profiles did not conform to any of the known peak shapes indicating that they are the sum of a number of overlapping peaks. Several techniques have been used to determine the exact number of overlapping peaks such as peak fitting, peak shape analysis and spectral deconvolution. The results indicate that the profiles are the sum of five C–N stretching bands. The five bands were attributed to the existence of the C–N vibrators in the cavities of different Mb-CN conformational states. The variations in the C–N stretching frequency were interpreted in term of the variation in polar interactions between the bound cyanide ion and the surrounding protein in these states.
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