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Long range electron transfer in Ru-modified [2Fe-2S] ferredoxins
ELECTRONTRANSFER A()10
LONG RANGE ELECTRON TRANSFER [2Fe-2S] FERREDOXINS
E Llovd,
97
IN Ru-MODIFIED
A G Sykes
Department of Chemistry, The University, Newcastle upon Tyne NE1 7RlJ, U.K. Plant and algal [2Fe-2S] ferredoxins, are redox proteins which are widely distributed in biological systems (M,-10,500; 93-99 amino acids), [l]. In the oxidised form the active site consists of two high spin Fe(II1) atoms bridged by sulphide (2-) with two cysteine ligands completing the tetrahedral geometry, [2]. On reduction the Fe(II)Fe(III) form is generated (E" = -4OOmV), with reduction localised at one Fe centre. Also of interest from the crystal structure is the observation that a carbonyl O-atom is only 2.8A from C's one of the Fe's. The ~~~~ existence of isomer forms Fd I and Fd II is now well documented. Those of A.variabilis have been separated in this work using hydrophobic interaction chromatography. used to The complex [Ru(NH,),(H,0)12' is chemically modify surface histidines. The ease of modification of different residues can be understood in terms of residues. pK,'s of histidine Modification of the A.v. Fd I component at His16 has been carried out, and the product characterised by ICP atomic emission and NMR spectroscopy. Pulse radiolysis experiments with eWsq as reductant are used to generate Fe(II)Fe(III), thus allowing intramolecular electron transfer Fe(I1) Fe(II1) -+ Ru(II1) to be studied. Making due allow antes for bimolecular contributions from inter molecular rate processes, the intramolecular constant is 11.4 f 0.6~~~ at 2OY!, I = O.lOM. The direct edge to edge separation from the nearest cysteinyl S-atom of the active site to the imidazole ring is -19A. The mechanism of electron transfer over this distance driving force -500mV is of interest. CYS
A G Sykes, Metal Ions Biol Syst, 27, (1991). 2. H Matsubara et al, J Biochem, 90, 1763-73 (1981).
1.
LONG RANGE ELECTRON TRANSFER [2Fe-2S] FERREDOXINS
E Llovd,
97
IN Ru-MODIFIED
A G Sykes
Department of Chemistry, The University, Newcastle upon Tyne NE1 7RlJ, U.K. Plant and algal [2Fe-2S] ferredoxins, are redox proteins which are widely distributed in biological systems (M,-10,500; 93-99 amino acids), [l]. In the oxidised form the active site consists of two high spin Fe(II1) atoms bridged by sulphide (2-) with two cysteine ligands completing the tetrahedral geometry, [2]. On reduction the Fe(II)Fe(III) form is generated (E" = -4OOmV), with reduction localised at one Fe centre. Also of interest from the crystal structure is the observation that a carbonyl O-atom is only 2.8A from C's one of the Fe's. The ~~~~ existence of isomer forms Fd I and Fd II is now well documented. Those of A.variabilis have been separated in this work using hydrophobic interaction chromatography. used to The complex [Ru(NH,),(H,0)12' is chemically modify surface histidines. The ease of modification of different residues can be understood in terms of residues. pK,'s of histidine Modification of the A.v. Fd I component at His16 has been carried out, and the product characterised by ICP atomic emission and NMR spectroscopy. Pulse radiolysis experiments with eWsq as reductant are used to generate Fe(II)Fe(III), thus allowing intramolecular electron transfer Fe(I1) Fe(II1) -+ Ru(II1) to be studied. Making due allow antes for bimolecular contributions from inter molecular rate processes, the intramolecular constant is 11.4 f 0.6~~~ at 2OY!, I = O.lOM. The direct edge to edge separation from the nearest cysteinyl S-atom of the active site to the imidazole ring is -19A. The mechanism of electron transfer over this distance driving force -500mV is of interest. CYS
A G Sykes, Metal Ions Biol Syst, 27, (1991). 2. H Matsubara et al, J Biochem, 90, 1763-73 (1981).
1.