Spectroscopy tyrosyl radical

Structure of the Iron Center Formation of the Iron Center and Tyrosyl Radical Spectroscopy of the Diferric Iron Center Spectroscopy of the Tyrosyl Radical Redox Properties of the Iron Center Mixed-Valent Form of the Iron Center Diferrous Form of the Iron Center Inhibitors to Iron-Containing Ribonucleotide Reductase Methane Monooxygenase A. Spectroscopy of the MMOH Cluster X-Ray Structure of MMOH... 

Bar, G., M. Bennati et al. (2001). High-frequency (140-GHz) time domain EPR and ENDOR spectroscopy The tyrosyl radical-diiron cofactor in ribonucleotide reductase from yeast. J. Am. Chem. Soc. 123 3569-3576. 

M. Bennati, A. Weber, J. Antonie, D.L. Perlstein, J. Robblee and J. Stubbe, Pulsed ELDOR spectroscopy measures the distance between the two tyrosyl radicals in the R2 subunit of the E. coli ribonucleotide reductase, J. Am. Chem. Soc., 2003, 125, 14988. 

Since the phenoxyls possess an S = ground state, they have been carefully studied by electron paramagnetic spectroscopy (EPR) and related techniques such as electron nuclear double resonance (ENDOR), and electron spin-echo envelope modulation (ESEEM). These powerful and very sensitive techniques are ideally suited to study the occurrence of tyrosyl radicals in a protein matrix (1, 27-30). Careful analysis of the experimental data (hyperfine coupling constants) provides experimental spin densities at a high level of precision and, in addition, the positions of these tyrosyls relative to other neighboring groups in the protein matrix. 

One of the most powerful spectroscopic techniques for the detection and characterization of persistent and transient phenoxyls is time-resolved resonance Raman (RR) spectroscopy. Vibrational frequencies and the relative intensities of the resonance-enhanced bands have proven to be sensitive markers for tyrosyl radicals in proteins. For example, Sanders-Loehr and co-workers (31) detected the tyrosyl radical in native ribonucleotide reductase from Escherichia coli by a resonance-enhanced Raman mode at 1498 cm 1 that they assigned to the Ula Wilson mode of the tyrosyl, which is predominantly the u(C=0) stretching mode. 

Denysenkov, V. P., Prisner, T. F., Stubbe, J., and Bennati, M. (2006). High-field pulsed electron-electron double resonance spectroscopy to determine the orientation of the tyrosyl radicals in ribonucleotide reductase. Proc. Natl. Acad. Sci. USA 103, 13386-13390. 

Bollinger, J. M., Tong, W. H., Ravi, N., Huynh, B. H., Edmondson, D. E., and Stuhhe, J., 1994a, Mechanism of assembly of the tyrosyl radical-diiron(III) cofactor of E. coli rihonucleotide reductase II. Kinetics of the excess Fe reaction by optical, EPR, and M ssbauer spectroscopies. /. Am. Chem. Soc. 116 8015n8023. 

The power satnration occurs when the rate of absorption of microwave exceeds the rate at which the system returns to eqnilibrinm. A spectral parameter, R1/2, is used to describe quantitatively the microwave power saturation profile. In the RNR tyrosyl radical case, the R1/2 values at four representative temperatnres are given in Table 3. The most straightforward interpretation for the easily saturated radical spectra with very small P j2 values, as seen in M. tuberculosis R2, is that the tyrosyl radical is minimally influenced in its relaxation by the di-ferric clnster. This finding is reverse in mouse and yeast R2 proteins. To obtain the precise distance information in a biological system, advanced techniques such as ESSEM would be more pertinent than the continuous-wave EPR spectroscopy. 

Lukoyanov D, Barney BM, Dean DR, Seefeldt LC, Hoffman BM. Coimecting nitrogenase intermediates with the kinetic scheme for N2 reduction by a relaxation protocol and identification of the N2 binding state. Proc. Natl. Acad. Sci. U.S.A. 2007 104 1451-1455. Denysenkov VP, Prisner TF, Stubbe J, Bennati M. High-field pulsed electron-electron double resonance spectroscopy to determine the orientation of the tyrosyl radicals in ribonucleotide reductase. Proc. Natl. Acad. Sci. U.S.A. 2006 103 13386-13390. Schiemann O, Prisner TF. Long-range distance determinations in biomacromolecules by EPR spectroscopy. Quarterly Rev. Biophys. 2007 40 1-53. 

---