| Autor: |
Doyle L; School of Chemistry, Trinity College Dublin, The University of Dublin, College Green, Dublin 2, Ireland., Magherusan A; School of Chemistry, Trinity College Dublin, The University of Dublin, College Green, Dublin 2, Ireland., Xu S; Department of Chemistry and Centre for Metals in Biocatalysis, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States., Murphy K; School of Chemistry, Trinity College Dublin, The University of Dublin, College Green, Dublin 2, Ireland., Farquhar ER; Case Western Reserve University Center for Synchrotron Biosciences, National Synchrotron Light Source II, Brookhaven National Laboratory Upton, New York 11973, United States., Molton F; CNRS UMR 5250, DCM, Univ. Grenoble Alpes, Grenoble F-38000, France., Duboc C; CNRS UMR 5250, DCM, Univ. Grenoble Alpes, Grenoble F-38000, France., Que L Jr; Department of Chemistry and Centre for Metals in Biocatalysis, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States., McDonald AR; School of Chemistry, Trinity College Dublin, The University of Dublin, College Green, Dublin 2, Ireland. |
| Abstrakt: |
In the postulated catalytic cycle of class Ib Mn 2 ribonucleotide reductases (RNRs), a Mn II 2 core is suggested to react with superoxide (O 2 ·- ) to generate peroxido-Mn II Mn III and oxo-Mn III Mn IV entities prior to proton-coupled electron transfer (PCET) oxidation of tyrosine. There is limited experimental support for this mechanism. We demonstrate that [Mn II 2 (BPMP)(OAc) 2 ](ClO 4 ) ( 1 , HBPMP = 2,6-bis[(bis(2 pyridylmethyl)amino)methyl]-4-methylphenol) was converted to peroxido-Mn II Mn III ( 2 ) in the presence of superoxide anion that converted to (μ-O)(μ-OH)Mn III Mn IV ( 3 ) via the addition of an H + -donor ( p- TsOH) or (μ-O) 2 Mn III Mn IV ( 4 ) upon warming to room temperature. The physical properties of 3 and 4 were probed using UV-vis, EPR, X-ray absorption, and IR spectroscopies and mass spectrometry. Compounds 3 and 4 were capable of phenol oxidation to yield a phenoxyl radical via a concerted PCET oxidation, supporting the proposed mechanism of tyrosyl radical cofactor generation in RNRs. The synthetic models demonstrate that the postulated O 2 /Mn 2 /tyrosine activation mechanism in class Ib Mn 2 RNRs is plausible and provides spectral insights into intermediates currently elusive in the native enzyme. |
