While sitting in my seat listening to Dr. Coon, I did some “fast numerology” with the mechanism proposed by Dr. Coon on a two-electron reduction of cytochrome P-450, and the numbers just didn’t seem to add up. Before performing this numerology, I shall have to define terms. Let us assume that ferric heme is at oxidation state III, ferrous heme is at oxidation state II, molecular oxygen at oxidation state IV (because four electrons are required to reduce oxygen to water), superoxide anion at oxidation state III and peroxide at oxidation state II. The standards for this system, atomic iron and water, are each defined as oxidation state zero. To begin with, if we are to believe Dr. Coon’s mechanism, it means that cytochrome P-450 in the resting state starts in the reaction cycle at oxidation state III. We know that is true since the protein has the EPR of an S = 1/2 low spin ferric heme. If two reducing equivalents are added (as Dr. Coon proposes) this means that the protein is now at the formal oxidation state of one. If molecular oxygen having an oxidation state of IV is now added (we know that oxygen is required for this reaction), the formal oxidation state of the hypothetical protein-oxygen complex is V.
KeywordsSoret Band Formal Oxidation State Ferric Heme Iron Iron Absolute Spectrum
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- 1.Sharrock, M., Munck, E., Debrunner, P., Lipscomb, J. D. Marshall, V. and Gunsalus, I.C., Proc. Nat. Acad. Sci.U.S.A.70 (1972).Google Scholar