X-ray absorption studies of intermediates in peroxidase activity |
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| Authors: | B Chance L Powers Y Ching T Poulos G R Schonbaum I Yamazaki K G Paul |
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| Affiliation: | 6. Department of Biochemistry/Biophysics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104 U.S.A.;1. AT&T Bell Laboratories, Murray Hill, New Jersey 07974 U.S.A.;2. Science & Technology Center, Genex Corporation, Gaithersberg, Maryland 20877 U.S.A.;3. St. Jude Childrens Research Hospital, Memphis, Tennessee 38101 U.S.A.;4. Biophysics Division, Research Institute of Applied Electricity, Sapporo, Japan;5. Department of Physiological Chemistry, Umea University, 901 87 Umea, Sweden |
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| Abstract: | The structures of the enzyme-substrate compounds of peroxidases and catalase determined by X-ray absorption spectroscopy are presented. The valence state of the iron in Compounds I and II is determined from the edge to be higher than Fe+3. A short Fe-Ne (proximal histidine) distance is observed in all forms except Compound II, forcing the Fe-Np average distance to be long, a result which differentiates the peroxidases from the oxygen transport hemoproteins and plays a pivotal role in the mechanism. A correlation is shown between the ratio of peaks in the low k (ligand field indicator ratio) region, the Fe-Np (heme pyrrole nitrogen) average distance, and the magnetic susceptibility, which provides a sensitive indicator of spin state. The mechanism of H2O2 reduction is shown by analysis of the structural changes observed in the intermediates. Possible relationship of these compounds to that of the peroxidatic form of cytochrome oxidase is suggested by these results. |
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| Keywords: | To whom correspondence should be addressed. |
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