Protein-heme interactions in heme-proteins: cytochrome C.

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Abstract
Insofar as the Soret transition derives its rotational strength from coupling with protein transitions, the rotational strengths of the protein transitions were altered in a reciprocal manner governed by the sum rule. Retention of the degeneracv of the Soret transition in myoglobin and hemoglobin, as measured by the intensity of the Soret band and the simplicity of the Soret Cotton effect, indicates that the chromophore has retained its inherent symmetry and therefore supports the proposition that a substantial contribution to the rotational strength of the Soret transition in these heme-proteins arises from coupling with protein transitions. Interpretation of the cytochrome c data based solely on a polypeptide or simple protein model leads to an apparent contradiction which is resolved by consideration of coupling of heme and protein transitions. The reciprocal relations required for this coupling are noted and the expected thermodynamic relations are found. Evidence was presented for the coupling of protein and heme transitions in cytochrome c.