RESONANCE RAMAN-SPECTROSCOPIC STUDIES OF THE NITRIC-OXIDE ADDUCTS OF COBALTOUS-RECONSTITUTED MYOGLOBIN AND HEMOGLOBIN

Resonance Raman spectra of the nitric oxide adducts of cobaltous-reconstituted myoglobin and hemoglobin were measured using 406.7-nm excitation. The nu(N-O), nu(Co-NO), and delta(Co-N-O) modes were located at 1613, 576, and 367 cm-1, respectively. The band assignments were secured by a normal-mode analysis of their frequencies and isotopic shifts upon substitution of natural-abundance nitric oxide with (NO)-N-15-O-16, (NO)-N-14-O-18, and (NO)-N-15-O-18. The slightly higher nu(Co-NO) and dramatically lower delta(Co-N-O) frequencies compared to those of the Fe(II)-NO linkage were explained on the basis of the consideration of both the bonding interaction between the central metal ions and the bound nitric oxide and the kinematic effect imposed by their significantly different bonding geometries.