MOLECULAR PROBES OF THE MECHANISM OF CYTOCHROME P-450

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The cytochrome P-450 of lung, liver, kidney, and epithelial tissue are known to play a central role in carcinogen activation, drug and xenobiotic detoxification and steroid and prostaglandin metabolism. The goals of this program are to elucidate the organic and inorganic chemistry of the processes mediated by cytochrome P-450 referred to collectively as oxygen- activation and substrate oxygenation. Our two-pronged approach has been (i) to employ substrates for cytochrome P-450 designed to reveal the nature of unseen intermediates and (ii) to develop model systems as chemical paradigms for these processes. An important aspect of these studies has been the direct comparison of enzymic and model reactions in the same laboratory. Specific activities proposed for the next grant period are: 1. Structure and Reactivity of Oxygenated Iron Porphyrins. The structure and interconversions of oxygenated iron porphyrin complexes continue to afford insight regarding the nature of the chemical events referred to as oxygen activation. We plan to prepare hydroperoxoiron(III) porphyrin complexes and related oxygenated species and observe their conversion to reactive complexes such as oxoiron(IV) porphyrin cation radicals. We will also explore strategies for the preparation of similar complexes with the biologically relevant thiolate ligation of the heme iron. 2. P-450 MOdels in Reconstituted Membranes. We plan to use synthetic and semi-synthetic phospholipid assemblies to model and understand the electron transfer events on P-450 action in membrane environments. Specifically, we will: (1) devise model membrane- porphyrin systems which can facilitate the study of the elusive iron(III)- thiolate coordination environment; (2) explore methods of differentiating the spatial orientation of membrane bound porphyrins and related redox components toward an understanding of vectorial processes in general; (3) explore our very recent finding that membrane bound redox enzymes such as cytochrome P-450 reductase, cytochrome b5, and pyruvate oxidase can communicate effectively with synthetic membrane redox partners. 3. DNA as a Substrate; Selective Reactions of Double-Stranded and Single- Stranded DNA. We plan to design water-soluble metalloporphyrins and related non-porphyrin metal complexes and to explore selective DNA and RNA strand cutting with these species. The effort may result in reagents for the selective, oxidative cleavage of oligonucleotides and may provide the basis for new families of antitumor and antiviral compounds based on the oxometal chemistry of cytochrome P-450. We plan also to study the DNA cleavage reactions of derivatives of cationic porphyrins with two metal coordinating appendages and to explore interactions of the species with ferritin mRNA.