ROLE OF THE POLARITY OF THE HEME ENVIRONMENT FOR THE CO STRETCH MODESIN CYTOCHROME P-450CAM-CO

The CO stretch mode of various substrate complexes of cytochrome P-450 cam-CO was measured using FT infrared spectroscopy, At room temperatur e most of the complexes shaw a single, but often asymmetric infrared b and. The representative wavenumber of this band for the various comple xes increases when the high-spin content, induced by the substrates in the oxidized protein, decreases. Additionally, the increase of the CO stretch wavenumber (1939 to 1956 cm(-1)) correlates with the decrease of the Soret band wavenumber (22 440 to 22 373 cm(-1)). It is suggest ed that the polarity of the heme pocket is modulated by the substrates due to changed accessibility of the heme environment for water molecu les. The increased water content compensates positive electrostatic po tentials near the CO ligand, which results in loosening the contact of CO to the I helix.