A carbon monoxide derivative of ruthenium (II) myoglobin probe of heme protein conformation.

A synthetic carbon monoxide complex of ruthenium (II) myoglobin has been reconstituted from apomyoglobin and the carbon monoxide of ruthenium (II) mesoporphyrin IX. This synthetic myoglobin complex shows an absorption spectrum with normal Soret and beta bands, and a split alpha band. The alpha-band splitting is not observed in the spectrum of the carbon monoxide derivative of ruthenium (II) mesoporphyrin IX in pyridine, even though the width of the alpha band in pyridine is narrower than in theprotein. The separation between two alpha bands in the spectrum of the protein is reduced from 7.5 to 6 nm in the presence of 2 M NaCl. This observation is interpreted in terms of perturbation of concentrated NaCl on the protein. The separation between the maxima of two alpha bands in the spectrum of the ruthenium (II) myoglobin also becomes smaller with decrease in pH from 7 to 4.5, and this process involves the distal histidine. The alpha band splitting in this protein complex is interpreted in terms of rhombic distortion of the square planar symmetry of the metal porphyrin in the protein.