FTIR investigation of the conformational properties of the cyanide bound human hemoglobin

Infrared spectra at 4 cm(-1) resolution of the cyanide ligated human methemoglobin (Hb-CN) were examined in the C-N 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-(CN)-C-12-N-15 and 2073, 2077 and 2081 cm(-1) for Hb-(CN)-C-13-N-14. 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 C-N stretching bands is consistent with C-N vibrators residing in different environment and support the hypothesis that Hb-CN assumes multiple conformers under the conditions studied. (C) 2002 Elsevier Science B.V. All rights reserved.