| Autor: |
J. Ling, M. Sahlin, B.M. Sjöberg, T.M. Loehr, J. Sanders-Loehr |
| Rok vydání: |
1994 |
| Předmět: |
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| Zdroj: |
Journal of Biological Chemistry. 269:5595-5601 |
| ISSN: |
0021-9258 |
| DOI: |
10.1016/s0021-9258(17)37503-8 |
| Popis: |
The formation of the iron-radical cofactor in the R2 subunit of ribonucleotide reductase has been monitored by resonance Raman spectroscopy. The differrous cluster in reduced R2 functions as a tyrosine oxidase; it uses O2 to oxidize Tyr-122 to a stable radical and results in an oxo-bridged diferric cluster. The Phe-122 mutant produces an identical dinuclear iron center and provides a simplified model for O2 activation. Oxidation with 18O2 results in quantitative incorporation of 18O into the diferric cluster as evidenced by the 13-cm-1 downshift in the Fe-O-Fe stretching vibration at 500 cm-1. Thus, O2 must be coordinated to the diiron center during O-O bond cleavage. When the Phe-208 adjacent to the diferous cluster is mutated to Tyr, reaction with O2 results in its oxidation to dihydroxyphenylalanine (DOPA-208) and subsequent coordination to Fe as a catecholate ligand. The Fe-O/(catecholate) stretching modes at 512 and 592 cm-1 shift by -13 and -8 cm-1, respectively, when the oxidation is performed in H(2)18O. These isotope shifts indicate that the second oxygen atom of DOPA-208 originates from H2O rather than O2. Taken together, our results are consistent with a mu-1,1-peroxide and a high valent iron-oxo species as reaction intermediates. A common pathway for oxygen activation by the related iron-oxo enzymes methane monooxygenase and fatty acid desaturase is proposed. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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