Dioxygen is the source of the mu-oxo bridge in iron ribonucleotide reductase

• Published in: The Journal of biological chemistry Vol. 269; no. 8; pp. 5595 - 5601
• Main Authors: JINSHU LING, SAHLIN, M, SJÖBERG, B.-M, LOEHR, T. M, SANDERS-LOEHR, J
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Society for Biochemistry and Molecular Biology 25-02-1994
• Subjects: Analytical, structural and metabolic biochemistry; Biological and medical sciences; Catechols - chemistry; Enzymes and enzyme inhibitors; Escherichia coli; Fundamental and applied biological sciences. Psychology; Iron - chemistry; Mutation; Oxidoreductases; Oxygen - chemistry; Ribonucleotide Reductases - chemistry; Ribonucleotide Reductases - genetics; Spectrum Analysis, Raman; Oxygen; Enzyme; Activation; Iron; Oxidation; Raman spectrometry; Cofactor; Reductase
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/s0021-9258(17)37503-8

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.