Dynamics of heme in hemoproteins: proton NMR study of myoglobin reconstituted with iron 3-ethyl-2-methylporphyrin.
Résumé
The asymmetric 3-ethyl-2-methylporphyrin iron complex was synthetized and inserted into apomyoglobin. UV-visible spectroscopic studies demonstrated the capacity of iron to coordinate different exogenous axial ligands in ferrous and ferric forms. The position of synthetic heme into the hydrophobic pocket of the reconstituted myoglobin was investigated by ((1))H NMR spectroscopy. In absence of exogenous ligand, signals of the synthetic prosthetic group were not detected, suggesting a rotational disorder of the synthetic porphyrin into the heme pocket. This direct interconversion behavior is favored since site-specific interactions between the poorly substituted heme and protein in the chiral hydrophobic cavity were weak. Complexion of cyanide to the iron allowed to quench partially the heme reorientation and two interconvertible forms, around the meso-Cα-Cγ axis, were detected in solution.