IRON L-EDGE X-RAY-ABSORPTION SPECTROSCOPY OF MYOGLOBIN COMPLEXES AND PHOTOLYSIS PRODUCTS

We demonstrate the first application of L-edge X-ray absorption spectr oscopy (XAS) to the electronic characterization of biological photolys is products. The experimental L-edge XAS spectra of deoxymyoglobin (de oxy Mb), oxymyoglobin (MbO(2)), carbonmonoxymyoglobin (MbCO), and the low-temperature photoproducts (MbCO and Mb*O-2) are presented and com pared to simulated spectra using a ligand field multiplet calculation. This analysis indicates that MbCO and MbO(2) are both low spin and do es not support some previous studies which suggest that MbO(2) has an intermediate spin. Both photoproducts, MbCO and Mb*O-2, are different from deoxy Mb in the Fe-II electronic structure. In addition, differe nt low-temperature photolysis intermediates are suggested for MbCO and MbO(2). The L-edge XAS spectra for Fe-III in aquometmyoglobin (met Mb ) and azidomet myoglobin (MbN(3)) provide a comparison of the ferrous versus ferric myoglobin species. Finally, the special advantages of us ing soft X-ray absorption spectroscopy for understanding the electroni c transitions coupled to photolysis-induced structural changes are dis cussed.