APPLICATION OF SPECTROPOLARIMETRY TO DETECT CHANGES IN THE ENVIRONMENT OF THE HEME OF CYTOCHROME c.
Creators:Urry, Dan W.
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Publisher:Ohio State University
The very large electric dipole transition moment characteristic of the Soret band of heme compounds would be expected to couple with other strong electric transitions in its vicinity. When the environment of the heme is disymmetric, the Cotton effects resulting from this transition may be used to detect changes in that environment. The iron porphyrin of cytochrome c is covalently bound to the protein by two thiol ether bridges, the sulfurs arising from cysteine residues. In addition the fifth and sixth coordination positions of the hemato porphyrin are occupied by ligands arising from the protein. It is, therefore, possible to treat this protein in numerous ways and to correlate changes in the heme environment, as reflected in the anomalous dispersion in the Soret region, with changes in the secondary and tertiary structure of the protein as determined by the Cotton effects characteristics of helical and random coil protein conformations. Thus by the addition of denaturing agents, iron binding ligands and by varying the temperature and pH, it is possible to determine gross differences in the environment of the heme in its two oxidative state. The anomalous dispersion in the Soret region of ferricytochrome is readily altered by raising the temperature, and by addition of quanidine HCl or imidazole whereas in ferrocytochrome the Soret Cotton effects are affected very little or not at all by varying these parameters. The relation of these environmental changes to the quantum states will be considered.
Author Institution: Conant Chemical Laboratory, Harvard University
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