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| {{STRUCTURE_1s13| PDB=1s13 | SCENE= }} | | {{STRUCTURE_1s13| PDB=1s13 | SCENE= }} |
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| '''Human Heme Oxygenase Oxidatition of alpha- and gamma-meso-Phenylhemes'''
| | ===Human Heme Oxygenase Oxidatition of alpha- and gamma-meso-Phenylhemes=== |
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| ==Overview==
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| Human heme oxygenase-1 (hHO-1) catalyzes the O2-dependent oxidation of heme to biliverdin, CO, and free iron. Previous work indicated that electrophilic addition of the terminal oxygen of the ferric hydroperoxo complex to the alpha-meso-carbon gives 5-hydroxyheme. Earlier efforts to block this reaction with a 5-methyl substituent failed, as the reaction still gave biliverdin IXalpha. Surprisingly, a 15-methyl substituent caused exclusive cleavage at the gamma-meso-rather than at the normal, unsubstituted alpha-meso-carbon. No CO was formed in these reactions, but the fragment cleaved from the porphyrin eluded identification. We report here that hHO-1 cleaves 5-phenylheme to biliverdin IXalpha and oxidizes 15-phenylheme at the alpha-meso position to give 10-phenylbiliverdin IXalpha. The fragment extruded in the oxidation of 5-phenylheme is benzoic acid, one oxygen of which comes from O2 and the other from water. The 2.29- and 2.11-A crystal structures of the hHO-1 complexes with 1- and 15-phenylheme, respectively, show clear electron density for both the 5- and 15-phenyl rings in both molecules of the asymmetric unit. The overall structure of 15-phenylheme-hHO-1 is similar to that of heme-hHO-1 except for small changes in distal residues 141-150 and in the proximal Lys18 and Lys22. In the 5-phenylheme-hHO-1 structure, the phenyl-substituted heme occupies the same position as heme in the heme-HO-1 complex but the 5-phenyl substituent disrupts the rigid hydrophobic wall of residues Met34, Phe214, and residues 26-42 near the alpha-meso carbon. The results provide independent support for an electrophilic oxidation mechanism and support a role for stereochemical control of the reaction regiospecificity.
| | The line below this paragraph, {{ABSTRACT_PUBMED_15297453}}, adds the Publication Abstract to the page |
| | (as it appears on PubMed at http://www.pubmed.gov), where 15297453 is the PubMed ID number. |
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| | {{ABSTRACT_PUBMED_15297453}} |
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| ==About this Structure== | | ==About this Structure== |
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| [[Category: Heme degredation]] | | [[Category: Heme degredation]] |
| [[Category: Heme oxyhenase-1]] | | [[Category: Heme oxyhenase-1]] |
| ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sat May 3 08:09:42 2008'' | | |
| | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jul 28 03:51:58 2008'' |
