Abstract
Infrared spectra at 4 cm −1 resolution of the cyanide ligated human methemoglobin (Hb-CN) were examined in the CN stretching region. The FTIR spectra of hemoglobin ligated with the various isotopomeric forms of the cyanide ion support the existence of three conformational states for Hb-CN. In potassium phosphate buffer at pH of 7.5, the three bands were observed at 2116, 2122 and 2127 cm −1 for natural abundance Hb-CN. These bands shift to 2086, 2091 and 2095 cm −1 for Hb- 12 C 15 N and 2073, 2077 and 2081 cm −1 for Hb- 13 C 14 N . Two extra bands have been identified in the IR spectra of solid Hb-CN in KBr pellets. The peaks persist in the pH range between 3.5 and 10.5 with small changes in frequency and intensity. The appearance of several CN stretching bands is consistent with CN vibrators residing in different environment and support the hypothesis that Hb-CN assumes multiple conformers under the conditions studied.
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