Mossbauer rapid freeze-quench

The time-dependent, rapid freeze-quench Mossbauer experiments with M. capsulatus (Bath) (51) indicate that decay of the peroxo species proceeds with the concomitant formation of another intermediate, named compound Q. This intermediate, observed in both the M. tri-chosporium OB3b (69, 70) and M. capsulatus (Bath) (51, 71) MMO systems by Mossbauer and optical spectroscopy, decays faster in the presence of substrates. Such behavior indicates that this intermediate is probably on the kinetic reaction pathway for hydroxylation (51, 70). 

CEMS = conversion electron Mossbauer spectroscopy DFT = density functional theory EFG = electric field gradient EPR = electron paramagnetic resonance ESEEM = electron spin echo envelope modulation spectroscopy GTO = Gaussian-type orbitals hTH = human tyrosine hydroxylase MIMOS = miniaturized mossbauer spectrometer NFS = nuclear forward scattering NMR = nuclear magnetic resonance RFQ = rapid freeze quench SAM = S -adenosyl-L-methionine SCC = self-consistent charge STOs = slater-type orbitals TMP = tetramesitylporphyrin XAS = X-ray absorption spectroscopy. 

Stopped-flow UV-vis absorption and rapid freeze-quench (RFQ) EPR and Mossbauer studies have shown that the reaction pathway diagrammed in Figure 4 for formation of the tyrosyl radical is essentially accurate except that the diiron(IV) species labeled Q in Figure 4 has never been detected in R2. Instead, an intermediate labeled U (not shown in Figured), occurring prior to X, has properties consistent with a protonated tryptophan cation radical. This radical may shuttle an electron from an external donor to the diiron site in order to reach intermediate In... 

Krebs C, Price JC et al (2005) Rapid freeze-quench 57Fe Mossbauer spectroscopy monitoring changes of an iron-containing active site during a biochemical reaction. Inorg Chem 44 742-757... 

In an examination of the literature dealing with the study of non-aqueous solutions, it is striking that there is virtually no experimental procedure for the investigation of matter that has not been employed to study solvation or other processes involving solvent effects. Scarcely does a new method appear in the arsenal of the analyst than it is applied to this field of solution chemistry. This tendency is well shown by the example of typical methods, developed for the investigation of solid substances, such as Mossbauer spectroscopy and ESCA. The application of these to the study of solvation processes was made possible by the elaboration of the technique of quenching solutions by rapid freezing. 

The rapid-quench method [78] was used in Ref. 83 to analyze the mechanism of a bacterial phenylalanine hydroxylase, a mononuclear nonheme iron protein that uses tetrahydropterin as the source of the two electrons needed to activate O2 for the hydroxylation of phenylalanine to tyrosine. Mossbauer spectra of samples prepared by freeze-quenching the reaction of the complex enzyme— Fe(ll)-phenylalanine-6-methyltetrahydropterin with O2 revealed the accumulation of an intermediate at short reaction times (20-100 ms). The Mossbauer parameters of the intermediate (3 = 0.28mms, A q= l.26mms ) suggested it to be a high-spin Fe(IV) complex similar to those that have previously been detected in the reactions of other mononuclear Fe(ll) hydroxylases. 

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