Ribonucleotide reductase spectroscopic characterization

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. 

The binuclear iron unit consisting of a (p,-oxo(or hydroxo))bis(p.-carboxylato)diiron core is a potential common structural feature of the active sites of hemerythrin, ribonucleotide reductase, and the purple acid phosphatases. Synthetic complexes having such a binuclear core have recently been prepared their characterization has greatly facilitated the comparison of the active sites of the various proteins. The extent of structural analogy among the different forms of the proteins is discussed in light of their spectroscopic and magnetic properties. It is clear that this binuclear core represents yet another stractural motif with the versatility to participate in different protein functions. 

The two-electron reduction of the diferric forms of hemerythrin (51), ribonucleotide reductase (27, 50), and methane monooxygenase (31) yields dioxygen-sensitive diferrous forms of the proteins. All three can be generated by dithionite treatment of the corresponding diferric forms, although the RRB2 reduction requires methyl viologen as mediator. The Fe(II) oxidation state is more difficult to probe spectroscopically, and only recently have methods been developed that allow this state to be characterized further. 

Atta M, Nordlund P, Aberg A, Eklund H, Fontecave M. 1992. Substitution of Manganese for Iron in Ribonucleotide Reductase from Escherichia coli spectroscopic and Crystallographic Characterization. JBiol Chem 267 20682-20688. 

Ravi N, Prickril BC, Kurtz Jr DM, Huyiih BH. 1993. Spectroscopic characterization of Fe-reconstituted rabrerythrin, a noriheme iron protein with structural analogies to ribonucleotide reductase. Biochemistry 32 8487-8491. 

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