A current theme in bio-inorganic chemistry is oxygen activation by heme enzymes such as cytochrome P-450, cytochrome oxidase, peroxidase and catalase. We will be continuing our project using resonance Raman spectroscopy as a probe to contribute to the understanding of the mechanisms of oxygen activation in peroxidases and catalases. peroxidases and catalases are important models for the mechanism of cytochrome P-450. Several types of the cytochrome P-450 enzyme are found in the liver, which oxidize toxic substances into hydrophilic material which can be more easily removed from the body. It is now believed that cytochrome P-450 is involved in the activation of certain substances into active carcinogenesis. Examples of these substances are polycyclic aromatic hydrocarbons, which are relatively new to the environment. Intermediate forms of cytochrome P-450 are believed to contain the heme group in highly oxidized states. Intermediate states of cytochrome P-450 involving oxidized hemes have not yet been spectroscopically observed. However, intermediate states of peroxidases and catalases, involving oxidized hemes, have been studied for many years. The mechanisms of peroxidases and catalases involve two intermediates known as compounds I and II. Compound I is two oxidation equivalents above the resting enzyme and contains an Fe(IV) porphyrin Pi-radical cation. It is proposed to obtain structural information about porphyrin Pi-radical cations in both peroxidases and catalases using rapid acquisition resonance Raman spectroscopy. Compound II is one oxidation equivalent above the resting enzyme and contains an Fe(IV) heme. It is now known that an activated oxygen atom is bound to the iron atom as an Fe(IV)=0 group in compound II. The resonance Raman Fe(IV)=0 frequency is markedly sensitive to environmental effects in the heme pocket. Since the Fe(IV)=0 group is the active oxidant in heme enzymes, its resonance Raman frequency will be used a probe to monitor the way heme enzyme reactivity is tuned. We will study these effects in various enzymes and those altered at specific sites by site-directed mutagenesis.
