Radicals iron

The mouse R2 radical is considerably less stable than the E. coli R2 radical (Nyholm et al., 1993). Strikingly, the iron ions are not very tightly bound to the mouse protein, and purified mouse R2 is obtained with only 0.1 Fe/R2 and has to be reconstituted before use (Mann et al., 1991). This is probably an effect of the more open structure of the iron-radical site as seen from the crystal structure (Kauppi et al., 1996). Possibly, the relatively high midpoint potential of ca. lOOmV for the mouse diiron site also affects the radical stability. 

Kauppi, B., Nielsen, B. A., Ramaswamy, S., Kjller Larsen, I., Thelander, M., Thelander, L., and Eklund, H., 1996, The three-dimensional structure of mammalian rihonucleotide reductase protein R2 reveals a more-accessihle iron-radical site than Escherichia coli R2. J. Mol. Biol. 262 706n720. 

A similar case of concurrence of one-electron transfer and nucleophilic addition is observed in the thermal ion-pair annihilation of CpMo(CO)3 anion with (dienyl)Fe(CO)3+ cations [84, 179]. Thus, spontaneous electron transfer (A et) occurs upon mixing of ( / -cyclohexadienyl)Fe(CO)3 with CpMo(CO)3 in acetonitrile to afford the transient 19-electron iron radical and the 17-electron molybdenum radical which both rapidly dimerize (Eq. 51). 

A rare redox reaction carried out by ETC catalysis is the disproportionation of bimetallic metal carbonyl complexes such as [MoCp(CO)3]2 containing a metal-metal bond, in the presence of a two-electron donor such as PMc3. In this typical example, the reaction leads to the ion pair [Mo Cp(CO)2(PMe3)2][Mo°Cp(CO)2]. The photolysis of the dimer gives the 17-electron iron radical [Mo Cp(CO)3] re-... 

The crystal structure of the mouse R2 RR has also been solved but it contained only one iron ion, maybe because in this enzyme the iron/radical site is more exposed to the solvent [72]. A recent report on the crystal structure of this mamma-Han R2 with a dinuclear cobalt center replacing iron foimd a different orientation for one of the glutamate Hgands when compared with the bacterial enzyme [73]. This could explain the increased labiHty of one of the iron centers. Because the substrate-binding site in R1 and the radical-generating site in R2 are far apart a... 

Hogbom M, Hnqne Y, Sjoberg B-M, Nordlrmd P. 2002. Crystal structure of the di-iron/radical protein of ribonucleotide reductase from Corynebacterium ammoniagenes. 

Saleh L, Krebs C, Ley BA, Naik S, Huynh BH, Bollinger Jr JM. 2004. Use of a chemical trigger for electron transfer to characterize a precursor to cluster X in assembly of the iron-radical cofactor of Escherichia coli rihonucleotide reductase. Biochemistry 43 5953-5964. 

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