Determination of the Raman tensor of the haem group in myoglobin by resonance Raman scattering in solution and single crystals

Abstract

We have measured the depolarization ratio and the excitation profiles of the Raman lines at 1,355 cm⁻¹, 1,564 cm⁻¹ and at 1,373 cm⁻¹, 1,580 cm⁻¹ in solutions of deoxy Mb and ferric MbCN, respectively, in the region between the Soret and the α, Β-bands. From their dispersion we have determined the tensor components of the Raman tensor by an extension of Loudon's theory, taking into account static distortions from the ideal D _4h -symmetry of the haem group, induced by haem-protein interactions and the interaction of the side-chains with the porphyrin skeleton (Schweitzer et al. 1984).

Analogous to the excitation profiles in solution, measurements on Mb single crystals yield intensities I _{a, b} which are related to the tensor components viewed in the laboratory system, spanned by the three orthogonal crystals axes a, b, c ^*. By using the structural data of the crystals and coordinate transformation from the system of the molecular coordinates into the laboratory system, the quantities I _{a, b} can be calculated by use of the tensor components determined from the solution data.

The values thus calculated and those which are determined experimentally from the single crystals are in good agreement. This confirms the theoretical approach of Schweitzer et al. (l984).