Proton Nuclear Magnetic Resonance Investigation of the Mechanism of the Reconstitution of Myoglobin That Leads to Metastable Heme Orientational Disorder
The nature of the initially formed complexes between sperm whale apomyoglobin and hemin has been investigated by 1H NMR for the purpose of elucidating the factors that give rise to heme orientational disorder in the reconstitution process. Selective removal of each of the two propionate side chains leads to an initial complex upon reconstitution (in the presence of a non-interacting organic solvent) with strong selectivity for the heme orientation which places the sole propionate into the position occupied by the 6-propionate group in the crystal structure. Hence the propionate contacts with apomyoglobin lead to the heme disorder about the α,γ-meso axis. Equilibration yields a unique heme orientation identical to that found in native Mb single crystals. Reconstitution of apomyoglobin with iron-free protoporphyrin yields only a single heme orientation within the time needed to obtain a NMR spectrum. However, this is concluded to result from rapid equilibration rather than from unique insertion of the porphyrin. The larger ring current for the des-iron myoglobin complex is interpreted in terms of protonation of the His F8 side chain that interacts with the porphyrin core. Pyridine is shown to interact strongly with cyanomet myoglobin, and the induced changes in hyperfine shifts show a spatial selectivity which suggests that pyridine intercalates on the proximal side of the heme. © 1989, American Chemical Society. All rights reserved.
Publication Source (Journal or Book title)
Journal of the American Chemical Society
La Mar, G., Pande, U., Hauksson, J., Pandey, R., & Smith, K. (1989). Proton Nuclear Magnetic Resonance Investigation of the Mechanism of the Reconstitution of Myoglobin That Leads to Metastable Heme Orientational Disorder. Journal of the American Chemical Society, 111 (2), 485-491. https://doi.org/10.1021/ja00184a014