Optical absorption of copper met--myoglobin complexes.

The optical spectrum in the visible and near ultraviolet [ 1 ] has been one of the most widely used tools in the study of proteins. The heme moiety, the active site of the hemoprotein, absorbs strongly the visible radiation, and usually presents three optical bands, (Y, /3 and y. These bands are attributed to electronic transitions of the porphyrin ring. There are also other bands, such as the charge transfer (C.T) ones, in the spectrum. In low spin complexes, only (Y, /3 and y bands are seen in the visible spectrum. The C.T. bands, on the contrary, he in the infrared region, because of their small energy. This is not the case in the high-spin complexes, where the C.T. lines are mixed with the normal electronic transitions, producing a complicated spectrum. Furthermore, in ferric hemoproteins and their derivatives, there is generally a thermal equilibrium between these two spin forms as determined by magnetic susceptibility and EPR measurements PI* The studies of the optical absorption bands for different myoglobin complexes (MbH20, MbF-, MbHCO;, MbCHa .CO;, MbNO: , etc.) [ 1 ] showed a correlation between their positions and intensities and the electronic and spin state of the iron ion. Nevertheless, the identification of the observed bands with