Proton nuclear magnetic resonance characterization of heme disorder in hemoproteins
A proton NMR method is described for determining the orientation of a porphyrin within the heme pocket of a hemoprotein. The pattern of the hyperfine-shifted heme methyl resonances in low-spin ferric model compounds is demonstrated to characteristically reflect the position of a localized low-symmetry perturbation on the π system. The specific assignments via deuteration of the two inconvertible sets of methyl resonances observed for deuteroporphyrin-reconstituted sperm whale metmyoglobin cyanide lead to the conclusion that the low-symmetry perturbations on the heme due to the apoprotein components by a 180°rotation about the α-γ meso axis. Hence the heme in the reconstituted myoglobin is 'disordered' in solution, and the altered functional properties of the reconstituted protein cannot be simply attributed to the local effect of the heme substituent. This NMR technique has applicability for determining the relative heme orientation in related hemoproteins, and may clarify the origin of doubling of heme resonances observed in several native hemoproteins.
Publication Source (Journal or Book title)
Proceedings of the National Academy of Sciences of the United States of America
la Mar, G., Budd, D., Viscio, D., Smith, K., & Langry, K. (1978). Proton nuclear magnetic resonance characterization of heme disorder in hemoproteins. Proceedings of the National Academy of Sciences of the United States of America, 75 (12), 5755-5759. https://doi.org/10.1073/pnas.75.12.5755